first you have to find a lube which is intended for plastic, I would look to teflon/silicones which are available in a dry version and therefore dont collect dust. I always wipe off excess as lube just needs to be inside. On Pulleys I use a penetrating lube and again wipe off excess. Reality is unless you live in a very dusty atmosphere its probably academic anyway.
BOB FREITAS
MILL
VALLEY,CA USA