The song "Dr. Feelgood" is a synth, not a bass. Possibly the whole album is, or was done by a ghost player.
Sixx was a rampaging smack addict "working" in a city notorious for its smack and strip bars during recording of that album, so was functionally useless, and many - probably most - albums of that era were done using ghost musicians, especially for drums, bass and guitar solos, from Warrant to Crue on down.
Plenty of threads on Sixx where you'd find much more info. than by starting a new one.