One of the reasons things get so dirty is we're dealing with tubes, little heater machines that need ventilation to survive. The ventilation also brings in dust, and it accumulates. I've used small paint brushes and acid brushes to stir things up for a c=vacuum with a crevice tool. Other advice from this list is to use waterless hand cleaner, the nonabrasive variety, and that worked well for my chassis.
Tubes, I always worried about those, but they are actually a lot more durable than we imagine, and often work pretty well even when they test "low."
Chris Campbell