If you don’t have the special tool for removing the top seal, it can be done without splitting the cases. Sharp drill bits are necessary and a bit of grease on them will help to hold the chips so they don’t fall into the roller bearing which is directly under the seal. Patience is also needed along with careful prying and pulling on the screws so nothing gets damaged.
Here’s a ’57 18 horse Fastwin having its top seal removed this way.
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