I am assembling a 408 stroker from parts I gathered back in 2001. I am using a new unopened FelPro gasket set. The rear main seal was in a separate sealed plastic bag and came with a little blue shoe horn that you are supposed to use to coax it into place.
Well these dropped right with little resistance. They look good but are significantly stiffer in composition than the oil pan gaskets in the same kit. I have the crank and caps in place but am wondering if I should use this new but 9 year old seal. I see Felpro lists 2 seals for the 360 one is made with Viton and more expensive QBS40651 and QBS40251 which is silicon I think, I think I know the answer . . . .. . buy an new one and dont take chances. Just wondering if there is a preferred brand or part number.

Thanks
Scott

I built a 408 two years ago and used the one that came with the "Fel Pro" kit. I've been chasing a leak at the back of the engine ever since. I just replaced the pan gasket for the second time and the rear seal this time with one I bought from Hughes although I'm sure you can get it elsewhere. The fel pro one was black and had one scraper ring on it and I could not see any issues with it when removed. The new one was Orange and had two scraper rings on it. I don't remember the exact name of it but so far no leaks.

Thanks,
Sorry you had such troubles. I laid the crank in last night and was aboutto torque it all down and I started thinking "what if". Im glad I asked.
Thanks for the insight and the info.
Scott

Just an update to the board in case anyone is looking for a rear main seal for a 360. The Felpro part number for the orange / brownish Viton rear main seal with two sealing lips for the LA 360 is BS40651 it's about $25.

The standard one that comes in the gasket set is rubber And the part number is BS40094 and is a single lip design. It's about $16.

Scott

when installing the seal I like to offset it in the block and cap so that the ends are not in the same position as the parting line of the cap and block. Helps greatly for sealing.