Berryman's parts cleaner works great but when thing get serious

That is a very good step by step systematic procedure! I really like my Berryman's Parts cleaner, glad I bought it. It's great for external gunk and goo removal, but heat is still your best friend when trying to get moving parts to move after years of hardened castor
locks them in place. Oh I've broke one or two con-rods (or crank pins) thinking..Oh, She's comming loose! OOps..., guess not!  In one of my last teardowns I used my trusty Wen soldering gun to "spot heat" the snout of the crankcase to heat the goo on the inside of the case between the crankshaft and case. Or in a extreme case I got the rear cover unscrewed and applied heat via the soldering tip up inside the crankcase in the bottom skirt of the piston until the 2 or 3 drops of oil on the top of the piston started to bubble! that'll break the castor grip!  Berrymans will discolor aluminum if parts are left in too long. I had a cylinder with a throttle sleeve stuck on it, I wasn't worried about discoloring,  so I left it soak for 2 days before the sleeve was loose enough to turn.

HEY! I forgot to mention in the last batch of Bee's I bought there were a couple of Unique ones.
The first one was a pristine version of the "taper head" screwed backplate Bee. The second was just a backplate that has the "notched" screen indentations holding the screen in place. SO, Cox must have used that for a short while, cause I checked all my others and this was the first one I've found that had the notches like the one you have. Cool!