These are a direct replacement Syncro part. It is not unusual for this part to go wrong and it effects your diff lock operation and vacuum system when it does. There is a diaphragm inside of them that can go hard, split and deteriorate so aways handy keeping one as a spare in your spares box anyway. When we have had these go wrong on the road they can often be heard buzzing when the rubber diaphragm has gone hard and lets air through.
VW Part number 433 862 117