You will probably have to use a small pin punch, or a very small chisel to carefully roll the seal away from the bore. Then pry it out. Trying to just pry it out with a screwdriver will just tear it up, and you will end up with a big mess. As already stated, it’s very easy to damage or break the seal bore (gearcase housing) . Those old 50’s seals are usually made of brass, and very hardy. I’ve rarely had one leak. I have seen several driveshaft seals that leak on the Big Twin motors though, but not on the smaller models.
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