Ok here's the article from GFTPM. It's a retrospective of the guitarists that Coverdale has sang with. These are Coverdale's thoughts.

Reprinted from Guitar For The Practicing Musician. February, 1990.

Chapter IV: John Sykes "Millionaires"

I poached a guy called Mel Galley, more for his voice, because he was like Glenn, but without the problems. We wrote some nice songs together; he was a real nice guy, but he had a very bad accident with his hand. I still wanted two guitarists, and my agent in Europe had recommended this guy, John Sykes. Whitesnake was headlining the "monsters of rock" in '84 and I put a Thin Lizzy album on, to check him out. There were always two guitarists in Lizzy, too, so it was difficult to know who was playing what, but it wasn't over-the-top good. John was a very good looking boy and nowhere near the guitarist he is now, but he was still interesting. I flew him over to Munich, where I was making the "Slide It In" album. I put on this old Little Willie John tune that i'd done with just a church organ, and me in a chapel singing "Need your love so bad..." I said to him "Take the vocal out; just play along with these passing chords." It's a very moving piece, but he really didn't know what to do with it. Cozy (Powell), Martin Birch, and everybody around was going, "No, no, no. Forget it." I couldn't let it go. At that time, it was hired hands, and he wanted too much money. I was also speaking to Adrian, who at that time was having a hit with "Burning Heart." Adrian said it was the most difficult decision he ever made, 'cause he was a major fan. I couldn't close the door on John, so I started talking to him again. I was totally unsupported by everybody I was involved with. Maybe it was a way to go, "I'll show you!" I don't know. Anyway, Mel broke his arm in two places, and we had to do five shows. It ended up that Jon Lord had to play harder than ever to cover spaces, and Sykes had to play harder than ever, and it was really good. They were the most exciting Whitesnake shows I'd had, to that point. I was very excited, so I made a very difficult decision about Mel. I said, "You're not in the band anymore. We'll have you, if you wish to still be involved, as a writer and on albums."
The label wanted to remix the album, with Keith Olson, which was when I first met Keith. I said, "You can, but I have a new guitarist, and I've got my old bass player back." The American album was my focus. I wanted them represented on the album, so they spent a couple of weeks working with Keith on the "Slide It In" album. Keith's a great radio mixer, but I was disappointed with a lot of the playing. Sykes' solos, like on "Slide It In," are not really that good. I wasn't in the studio with him, 'cause I'd almost washed my hands of it. I'd worked my nuts off with Martin Birch to give them a good album, so in essence, there are two Whitesnake albums. There's the American "Slide It In" album, with John, Mel, and Neil Murray, the bass player, and Jon Lord. The rest of the world was Mickey Moody, Mel Galley, Jon Lord, and a guy called Colin Hodgkinson. He was like a childhood hero of mine, when he was working with a jazz/rock trio called Backdoor.
I liked the European record, although the mix isn't as competent, isn't as radio oriented. At first, I was furious with the remixes. The only time I bought it was when I heard "Slow and Easy" and "Loving a Stranger," played to death when I was touring with Quiet Riot at the end of '84. One can only learn by keeping all the antennae out, and it was the first time I'd heard my voice right up here, and it worked. That's what came out of "Slide It In" and turned into the "Whitesnake" album. It was that focus to keep everything crisp.
All of the songs that John and I worked on came out of a five-day spurt, and ultimately made he and I millonaires. A Czechoslovakian film producer I know had a villa in a place about 30 minutes from San Tropez. We got a little ghetto-blaster with condenser mikes, because I loathe exotic demos. I said, "Let's not try to write a Whitesnake album." He'd written with Lizzy, of which I was totally unimpressed. I never got him involved for his writing ability. We just bounced off each other. We came up with much more than is actually featured. There were acoustic guitars, and the Rockman amplified through little speakers. John plays with a fabulous rock attitude. He hits, and the effort is evident at the end of a track. It was great. My stock quote was, "If he was 10% the person that he is as a musician, he would be easy to work with," but it was impossible. The biggest problem starts when he takes the guitar off. Actually, we fell out when we were working down there, and then kissed and made up, and he came back and brought Neil with him, so we worked with Neil on the tunes. The tunes were cool, John Kalodner at Geffen Records flipped, and we spent the summer of '85 auditioning drummers in the Valley, until I said, "That's it. The songs have been been ready for too long. I'm going nuts. I can't tell the difference between a guy who's good or bad. We're gonna use the Billy Idol/Keith Forsey method, and use a drum machine." Then Aynsley came into the picture, and he was the only one who had the energy to keep time, and keep up with the actual frenzy that was going on at the top. And it worked.
The most striking thing that I realized when we were in Vancouver, was John's frustration of not being able to get a sound. I think he expected to plug in and just get a sound. I came to the studio one day, and there was this whole monitor system, which was exactly the same as we'd used rehearsing in L.A. There he is with this huge rig. Mike Stone was going, "I've never had trouble getting a guitar sound with Schon or Brian May." I realized that John didn't have an identity. Regardless of whatever's been said in print, I fired John on the telephone and to his face. I had Adrian Vandenberg in the studio when John came to say "What's going on?" I said, "It's over. It's just over." He'd spent a fortune in the studio, on the guitars. He didn't support me when the producer, Mike Stone, refused to leave England to continue work on the project, and I, for tax reasons, am unable to go to England, so, you know, it was all compromised, all the time. This guy said that he wasn't going to do the guitars until I gave him a set amount of money, and I was already three million dollars in debt. In the end, it was just a mutual dislike for each other. There was a resentment that I was known and he wasn't. It was a very difficult thing. His favorite people are all rebels, in terms of thinking they're bulletproof, in terms of what they can do to their bodies, and not see how debilitating it is. I encouraged John and it was a situation I will never take away from. He played magnificently, but working with him was intolerable for me. He worked with me for the smallest period of time of anybody else within the Whitesnake framework, and made more money than all of them put together. There was a percentage that I would not have been able to accomplish without Sykes, but in my heart of hearts, I know there's a great deal more that he would not have been able to accomplish without my involvement