2000 VW Eurovan - A/C clutch plate missing and A/C compressor spindle/shaft appears to be stuck

I purchased the van with the A/C clutch plate missing. Took it to an A/C shop to get the clutch plate installed and they said that the A/C compressor is actually stuck (spindle/shaft is not turning) and that is why the clutch plate came off. They are saying that the compressor needs to be replaced, expansion valves replaced and the system flushed (to remove any debris) and recharged.

Does this sound right? Why would a compressor seize? Should the shaft on the compressor be able to rotate freely when the clutch is not engaged? Do I really need a flush and the other parts replaced? Just want to make sure I don't replace parts I don't need to.

Any input would really help!