440 rear main seal... thoughts

The seal comes with pretty good instructions as well and I used the Right Stuff brand sealer on the sides.

It looks like some blocks and certain seal retainer combos don’t properly align and are slightly offset in relation to the seal grove when centered on the block. A slight side to side offset is sometimes required and using the solid side seals forces the housing to be centered in the block and can push the seal off to the side and cause a leak. Just using RTV of some sort on the sides allows the seal retainer to self center if needed as the gap between the block and retainer can be slightly wider on one side if needed.

I checked the alignment on my block before installing the seal and it was slightly off but when pushed to one side it aligned perfectly.

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