Steve Henning told that story; where he and his other guitar player(or roommate, can't remember) went to tour the Charvel/Jackson factory and Grover gave them a tour...and pointed out Marq who was tearing it up with his new free(Ozzy purchased) Charvel. Grover told them "there's Ozzy's new guitar player!" and he was just killing it, playing amazing stuff effortlessly and also started playing the intro to Bark at the Moon..
He said that drug problems were rumored to be the reason he didn't actually play for Ozzy in the end.