You're right Rampy, I forgot to mention that. That's how I actually change the color of my balltop sticks. The red ones installed on my P360's in my uright MAME cab used to be blue. Those have lots of play on them without any signs of wear. The multiple clear coats protect the color coat pretty well. Maybe in another couple years I may need to touch them up if they start to wear, but I kind of doubt it since it's been 9 months already and they are still as good as when I painted them.
Regarding the Reunion sticks, the knob would just come off during normal play, I wasn't taking a wrench to it or anything. The shafts rotate fine, it just seems like the rapid moving of the joystick was enough for them to loosen up. The funny thing is, I've never heard of anyone else ever having this problem. And like Grasshopper mentioned, I bet most people don't even realize that the tops are removable.
Perhaps they were never torqued on properly from the manufacturer, too. Or perhaps I am the only one who ends up with the oddball crap and sees these things...
Anyway, I put a little Loc-Tite on the threads and they have been fine ever since.