Above all, make sure the repairer flushes the system properly. I've posted these photos of the "black death" before - the detritus left behind when a compressor seizes. The murky liquid in one photo is the first flush of the system after a new compressor was fitted. The other photo is the same liquid after standing for a week or so and shows what the liquid should look like. Even with a new condensor, flushing is essential - several flushes in fact - you don't want any of the black death getting back into your new, expensively-imported FS10 compressor.