I took my old Sea Dweller in to the local Rolex AD and had them mount a gen Superdome T-39, the last step in restoring it to all-original condition. They picked the best of my stash of crystals and put 'er together, and boy does she shine!
So yesterday I took her back for a pressure and seals test, and she failed immediately. Huh?? He decased the movement and ran the pressure check against the case/back/crystal/crown only, and there was a HUGE leak at the 5:00 position, where the ring compresses the crystal onto the case.
Inspection under a loupe revealed the case, rehaut and retention ring to be in perfect condition, so we concluded that the crystal itself is stiff, perhaps brittle, from age. She's no longer waterproof.
So it's the end of an era. This one served as the diving timer for an instructor and master diver, and has been on the bottom of every sea and ocean for almost 39 years. Now it's time to rest ... no more swimming for the old girl. Although I'll miss knowing that she's ready for anything I can throw at her, she earned it.