rear main leak

I've read that too but I'm not really getting how to seal the sides on the retainer with Right Stuff, does it mean that you use RS in the slot where the side seals should be or do you seal it on the inside or outside of the retainer?
My plan is to change seals with engine in the car just removing the oil pan, not so fun but I've seen it done by others.
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I was able to still use the side seal strips with the retainer while clocking the seal at 6&12 oclock. I have heard that sometimes you might not be able to get them on both sides. Even with the side strips I used right stuff on the retainer to the block as a double protection. If for some reason there's not enough room for one or both side strips just use right stuff on both sides of the retainer. Make sure the block and retainer are clean clean clean and no oil residue before applying RS. Brake clean should clean things up good for you. Doing the job in the car will be harder than on the stand, just more awkward. Good luck!