I would agree with Oly on this. Rope is the way to go.
What I noticed is the neoprene seal rides on a very thin edge on the crank. The cranks on these old 235's are not perfect. Mine had just a bit of pitting on the seal area. If I had used the neoprene it was sure to leak. The rope has a wider sealing surface and can accomodate imperfections better. The other thing I had noticed is that the neoprene did not sit in the slot in the cap or the block as well. I think they might even leak around the outside of the seal even if your crank was perfect.
Just my thought.
Brent
