In the off season, the cars are completely stripped down, body panels are removed, everything is pulled, and all of the components are tested. The exact test used varies from part to part, but tests include visual inspection, dye penetrant testing, magnetic particle testing, and radiography (X-ray). Any part that fails the test is either repaired or replaced. Some parts (fasteners, in particular) are simply replaced without testing. Damaged Fiberglas parts may be repaired or replaced, and are probably re-painted. Foam pads are replaced. Each car gets reassembled, gets a new set of wheels, and gets put back on the track in time for the next season.
--Dave Althoff, Jr.