If the compressor pulley is starting to lock, you may only need to replace the pulley - a lot cheaper than replacing the entire compressor. You still have to find the leak though. If the leak is at the compressor, such as a shaft seal, then yes, a complete rebuilt compressor and pulley is in order.

I'm pretty sure a/c compressors are compatible with both r12 and r134. Check first with the supplier to be absolutely sure.

I can understand why a mechanic wouldn't want a customer-supplied a/c compressor. He needs to guarantee his work. Plus he may have a relationship with his supplier. Shoud the a/c compressor crap out, it would be a lot more difficult (involved) to replace than say an alternator.

Sadly, your plight is rather typical of people who own older cars. Usually, when the owner sees the cost of repairing a/c on an older car, they opt to replace the car, even though it's otherwise running fine and serves the driver well. Cold a/c is important to a lot of drivers. This is also one of the more financially rewarding repairs a DIYer can do.

Perhaps you should contract and pay your mechanic to first do a diagnosis. He can find the leak and figure what needs to be replaced. If the machanic who charged the system with freon last time had any foresight, there's a good chance he probably put dye in the system. Only then can you make an informed decision.

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95 E320 Cabriolet, 169K