PowerPC :: G4 Munching On System 9 File

I had a mirror drive G4 1.25g, 1.5 g ram since it was brand new and it had problems from the start that just got worse over time. I still need to use it semi-regularly and so I would like to know if anyone here might have a clue what's going on. Of the long list of problems, I'll describe the ones that are the most frustrating! oh and by the way, I zapped pram and I have reinstalled everything from the original discs which made no difference at all.

1. When booting into 9 or classic, just about every other time or so I'll get a system error and I need to hold the power button to turn it off. Then I need to boot into X and replace the system file in the classic system folder (I already have a copy just for this purpose on the desktop) and then it will boot ok on the next run.
2. If I boot (9 or X) and don't touch the mac at all, it will hang up after about 10-15 minutes. If I reset and boot a second time, it won't freeze. So my practice for years has been: boot up, wait for the desktop to appear and restart immediately.
3. Many (but not all) applications fail to launch with an error (quitting unexpectedly), i.e. don't run at all. Some launch ok when the application is launched but quit when they're launched via a double click onto a related document.

How does that sound? Is there any hope for this machine at all? I would be eternally grateful for any solid pointers just as I'll be forever mad that I did not return this machine while it was still under warranty!