Rear main seals in oldsmobiles rarely go out, but in your case, a new rear main seal would be a good idea. The rope seals are used in all kind of Oldsmobile blocks, and I personally havent seen any fail. If you are really that worried about it, i would get ahold of mondello and ask for a rear main seal kit, or where to locate one. Usually their pretty congenial about things like that. However, if it was me, i would just use the roap seal and go.