Buying an old laser printer -- what will need to be replaced?

I would tend to think that parts that are generally considered consumables by a printer technician would be the ones to watch for. Parts such as pickup\feed rollers and fuser rollers\assemblies. I've never seen a PCB or motor go bad in all my years of using HP printers. The documented duty cycle for that model is 150,000 pages per month so 200,000 pages in its lifetime sounds like it's barely been used. Here are the complete specs:

HP LaserJet 8100 Series and 8100 MFP Printers - Product Specifications

Joeqwerty has already given good advice about the specific model, so I'll just add a little general advice.

When faced with the need to choose a printer I talk to the third party techs who service them for us. If the model has been out for a while I ask about the frequency they need servicing. I also ask what parts will cause the printer to be treated as a throw-away item and the normal life expectancy of those parts. e.g. A developer drum that costs nearly as much as a new printer and only lasts a few 100K pages makes me look for a different model. At the very least, find out what a service kit costs (and includes) before proceeding further with it.