The video I posted is for 6501 not 6510.
The 6510 has an extra screw/bolt attaching the lever to the rest of the mechanism, but it’s too tight to get a socket around, and too tight to loosen with a screwdriver.
Find a thin walled socket or a friend with a lathe (the best kind of friend).
Although it looks like you've been using a mismatched screwdriver. The right size and type and getting it on a bench / in a vice so you can apply a decent amount of downforce might shift it.
Hit a brick wall.
The video I posted is for 6501 not 6510.
The 6510 has an extra screw/bolt attaching the lever to the rest of the mechanism, but it’s too tight to get a socket around, and too tight to loosen with a screwdriver.
I tried.
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