Not just bad RAM, this machine was built 20 years ago, every component on the mainboard is a suspect.
Anecdotally, I was having issues with my Ultra 5, so I decided to replace all of the larger electrolytic capacitors. After that, I had no more lockups, no more segfaults, no more panics. It might be worth a look. If any of them are bulging, even just a little, then it might be time to replace.
John