The Slop question....
All RC cars have slop. Some have no slop when new, then develop slop very fast after a few race meets. Some kits you build and wonder why so much slop, yet the slop doesn't get any worse after a few races.
Gee, us racers are hard to please....
Yes, use shims. Or best, buy more parts and keep the companies in business.
They could make the plastic parts really hard and then we would complain when it breaks, too soft and we would saying the arm look bent. Last time people where complaining about sanding that 3mm spacer down to 2.8mm, but you had control over the amount of slop.
The Moral of the story : all good racers will use shims. (unless your a factory driver)
RC John : just double check your solder joints, that may be a causing the problem of over-heating.