Dave, we've been discussing this on another post with a gentleman who is currently rebuilding his 235. With the neoprene seal (or the rope seal either) it is important for your crank surface (the part riding against the seal) to be as smooth as possible. If yours is that way, then it tells me your seal may not be making good contact with the crank surface. About the only way I've found to solve that is to cut some shim pieces from self-adhesive foil (the kind the HVAC folks use) to pull it closer to the crank a bit. When you remove your old seal you might want to compare it end to end with a new one. That way you'll know if your crank is too rough. If so it will wear the seal down just like rubbing sandpaper on it. Good luck!

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end