I just lapped my valves on a cylinder because they were leaking and reused the stem seals. Should I put new stem seals or is it okay to reuse them?
Well, if you believe the seals are in good shape, there's nothing saying you can't reuse them. However, considering you have it all apart and the seals are relatively cheap considering the amount of time it would take to tear it all apart to replace these specifically, it only makes sense to replace them while you're in there. Time isn't a big deal, but when you consider where the seals are at, it does take a considerable amount to replace them. Realistically it is up to you whether they get replace. If I had any doubt about them, there would be new ones in place.