The wiring harness has been the biggest problem for me.
I haven't had any trouble with the A/C.
As far as the cooling system, I had to replace the reservoir (leaked at the flange, where the cap screws on to).
I had to have the calipers rebuilt (not unheard of for 150k miles)
I had to replace the Air Mass Sensor
Because the substandard wiring in the harness, extended into the ETA (electronic throttle actuator) I had to get a rebuilt one of those.
I had to replace the cabin blower motor and regulator.

They like to have their caps and rotors changed rather regularly at 15k mile intervals.

Expect about 23-24 mpg.

Bottom line....if the wiring harness looks good, then you should be safe. If it looks like it is going to need replacement, consider the fact that the ETA might need to be replaced too, and that's going to add up to some $$$ - Better make sure the price is right, in that case

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D