I got great advice here when I put the Best Gasket neoprene rear main seals (4519 S) in my 261. The advice, also found in the Tech Tips, included not getting oil on the lip part of the seal which has adhesive.

I also checked my 1973 Chiltons (1966-1973) to cover all bases. The instructions in Chiltons for rear main seals are virtually word for word as the Tech Tip! I find it funny that the only differences in the 5 bullet points are the phrases that say:

Chiltons: "revolve the upper half of the seal"
Tech Tip: "persuade the upper half of the seal to revolve"

I had to really, really, really "persuade" my seal!!!

No big deal here but I contacted Best Gasket about oil on the adhesive for their product. He said no worries.
Oil on the entire gasket is no problem. I don't think their gaskets have adhesive. I'm not recommending anything but I find all this interesting.

(I thought I had posted this already but can't find it.)

1948 3/4-Ton 5-Window Flatbed Chevrolet

34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.