I believe any 216-235-261 that has a "rubber" seal, the seal has been changed. When I built my engine in 1990, I was told rubber would not work in a 261, but the builder put rubber in without telling me. The first thing after I got the engine in the truck, the seal started leaking. I replaced it with a rope seal and haven't had a problem since. That's not to say a "rubber" seal wouldn't work, but a rope seal, properly installed and in my opinion, works best.
