If you replace the front main-seal, check the sealing surface carefully for a groove made by the lip seal. It there is one get a speedy sleeve by whatever name. Several are available. Much cheaper from the bearing houses than from NAPA or other FLAPS.
Changing the rear main is a whole weekend's work that can even result in changing the main-bearing shims if you're anal about such things. I ended up installing all new bearings, rods and mains, and the two seals on my now retired 235 truck engine. Don't start this in November unless you have a well-heated shop or live in the south. Don't ask how I know.
All the above was the result of chasing a rear main leaking into the clutch. I cut back the clearance on the rear main to stem the leak and decided to change them all. Engine was much quieter afterward.
