There's just no way. Who names a site canpharm.top? No reviews or information at all anywhere. The generic shopping images don't make me feel too comfortable either.
Although I did do a reverse image search, and it is a unique photo...
How are the caps? You should probably replace the few electrolytics on there, unless you got lucky and it doesn't have them. They usually only affect power, but you never know.
Also, could it be a RAM issue?
How tight is the belt? Guessing at this point in time, it would not be unusual for the belts to start stretching out and slipping. The carriage, at least as I remember it, has some resistance when you move it manually. I don't think there should be any belt slack.
If you want a very reliable Mac for 24hr usage, recap the logic board and PSU, or get it done by someone like Amiga of Rochester. Otherwise, for random whatever use, a logic board recap should be okay for now, unless the PSUs in these are known to go too?
Wasn't there some sort of issue installing OS 9 if you already had OS X installed, or was it the other way around? OS 9 required special drivers, but I can't remember if you can install it after installing OS X.
Is there a separate drive available to try a clean install?