Quoted from Doggy:still has the original battery.
Change that thing *immediately*. That battery has destroyed mountains of boards. When it leaks, it will be too late. It's best not to wait for an unstable 30-year-old time bomb to go off.
Wonky memory behavior can indicate power issues with the RAM chip, or a RAM chip failure. If it's an AMI-branded chip, chip failure is more likely, so it will need to be desoldered and replaced.