I thought I'd follow up with "what happened" on this topic. Turns out MER couldn't actually get the part either. They tried and tried but kept getting something that was not right. I ended up returning two different ($35 each) seals to them that were not right.
I tried the NAPA folks and other places that cater to trucking--but no go.
After a couple months and needing to get this transmission back onto the engine and in the boat--I went to a local industrial place (called Motion Control Inc) and looked through their SKF seal catalog to order a replacement seal. I ended up making the "minimum" order of 3 seals at $2.98/seal--including shipping/tax the total was around $18--so $6.00/seal
When I made the order at Motion Control, I also checked with the folks at Hurth yet again. They had something they "thought" would work--at about $55 plus shipping for 1 seal. I figured that was my back up if the Motion Control procured SKF seals didn't work. But all is well that ends well-- the seal was perfect and I have not one but TWO spares! at a very good cost savings.