Castellano switched to rhythm guitar and keyboards ( Castellano also filled in on lead guitar and vocals for an ailing Buck Dharma in two shows in 2005 ) , and the position of bassist was taken up by Rudy Sarzo ( previously a member of Quiet Riot , Whitesnake , Ozzy Osbourne and Dio ) , with the band employing Danny Miranda and Jon Rogers as guest bassists to fill in when Sarzo was unavailable .