Quote Originally Posted by m_c View Post
Provided you keep them clean and spinning, you shouldn't experience any major wear. You're only likely to experience major wear if things start sliding.
That is very true and easier to accomplish when you have bearings with way wipers sliding on rails.

So unless you enclose all the running gear in bellows you will embed dust to the tracks/bearings that will give very stiff jerky movement.

Very expensive are bellows and awkward to implement.

Phil