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It does look like the seal lip has got pushed out here:
The WS manual instructions probably aren't much help as they relate to using the tool. I will post them if you wish. Oddly, they state to install the seal dry?? I would never install an oil seal dry??
Only advice I can give is to use OEM, and to seat either flush or ~1mm in as already noted. I've encountered some fairly dubious aftermarket stuff for the MGB
Maybe not related but I have seen many failing rear main seals on Audi/VW where the root cause is the PCV. If the crankcase isnt ventilated the pressure will get out somewhere.