What is meant by a good valve seal? See my prior post. If your guides have excessive clearance and your seal is a PC type, that is all Viton, why would you expect them to accommodate the lateral valve stem movement without wearing that seal out in short order?
Viton seals won't handle the lateral movement caused by excessive valve stem clearance IMO. But I said that before. Why not provide a picture of the seals you are using?
