If you can get your wrists to fit without cutting, don't cut. More often people regret it later. Try the bathtub without cutting 1st, although not a lot of pressure there.My tendons aren't very prominent but maybe just enough to let in a little water. Perhaps I had the end of the seals too close to the wrist joint so small movements at the wrist created just enough opening.
Perhaps I'll try trimming the seals back just a little bit then donning the arms and submerging my wrist in a bathtub and moving my wrist around to see if I get any leaks.