If it's not one thing, it's another

[crod]

I think your issue is deeper than the car itself. The problem from what you posted so far seems more like someone with not enough knowledge of these cars attempted to fix it to sell (your mechanic). Now all sorts of problems, the ones you know of and the ones you may not know, are popping up.
My 2001 S has been bullet proof and if you get it in the hands of people that know these cars well, you will have no issues in most cases, especially if you take the proactive approach and replace stuff before anything happens. Good examples are replacing the IMS bearing every time the clutch is replaced, get the better water pump/thermostat and so on.
I would start looking for a good independent mechanic in your area. Many people here I bet can recommend you one.

CR