Looks like we have another one with video issues. As far the instability of the machine and the random crashes/freezes: this can be caused by a poor recap job or by faulty ram.

I've seen Macs crashing with bus errors, bombing, freezing,... due to faulty ram. I had a similar issue with my Mac IIFx a while ago, however the video issue isn't due to faulty ram. I would try replacing the Ram Simms, only use Bank A for testing with 4x known good one's and see how the machine behaves.