That sure was the problem back in the day and we used to massage the armatures with emery cloth and then scrape the mica ourselves too
Not much anymore. Like I said if his armature has a bad spot it won't stick or stall only at the bottom
True it is harder to get the window moving up from the bottom and that might make your argument hold H2O
So to test that you could just see if it will roll your arm up and off (the water drains out)