I just wanted to give everyone an update on what was up with my Dive Rite DIN-to-yoke adapter.
To recap, I had an issue with using the adapters on certain Sherwood tank valves. The piece that compresses the O-ring would only fit flush inside the valve recess if I tightened it down _really_ hard. Even then, there was a metal-on-metal grinding that occurred. Many times after dives, I found the adapter to be lodged/wedged so tightly into the recess that I had to rock the adapter from side-to-side with a lot of force to release it. According to Dive Rite, this is a known issue with older Sherwood tank valves (not the newer 5000 series). I encountered the incompatible Sherwood tank valves while on vacation in Bonaire (using Photo Tours Divers/Yellow Submarine as dive op).
Kathleen (Dive Rite Rep) was super nice about exchanging the adapters for the latest version of the product. As it turns out, I already had the latest version. I had purchased the model RG1225blk black-colored adapters from Dive Rite Express in July 2007. The official word from Dive Rite is that they are currently investigating the extent of the distribution of the incompatible Sherwood tank valves and whether this warrants a re-design of their DIN-to-yoke adapter.
So...that leaves me with 2 DIN-to-yoke adapters that will not fit certain older Sherwood tank valves. Before my next vacation, I will probably end up "investing" in some other brand (Trident or Poseidon) of adapter. I would hate to get stuck on a liveaboard and have to waste 10-15 minutes before each dive getting the adapter to seat properly onto the tank valve.
I hope that other DIN reg users out there find this info useful. My interactions with Dive Rite Customer Service were great, and they make some very good products (BP, harness kit, wings, etc.). However, I do take issue with the design of their DIN-to-yoke adapters. I can only hope that, once they run through their current inventory of adapters, they will re-tool the design (perhaps just slightly "thin out" the part of the adapter that compresses the O-ring).