The seals I use, as with most guys these days, are the rubber viton, with the little spring on the top. These do a great job of limiting oil, but not to good of a job, if that makes sense. Compared to the old scholl white teflon seals, that did to good a job in the begginging, then, not good enough after a short time. The viton material stays the same, for the life of the seal.
The reasoning for no seals from R&M, did this engine have a vacc pump? One reason could be simply they didn;t want any chance of sticking a guide. They may set the guides up tight, and leave the seal off for insurance. You can get away with a seal on the intake, and none on the ex. The vaccum on the intake stroke, can ands will suck oil in from the guides, it won;t do that on the ex.
Frank
Advanced Performance
www.get-ap.com