I have had very good luck in rehabbing mud flaps - front and rear - using sandpaper, steel wool, and a heat gun used for paint removal. Remove the flap from the car, bend and hold it to the desired shape, and use the gun to gently heat it. The plastic will soften and retain the deformation.

With front flaps, the problem is usually the material above the screws. This "flap-let" tends to collect mud and eventually move away from the fender liner. When rehabbing, bend the top "flap-let" material back toward the fender about 15-20 deg. beyond straight. When reinstalled on the fender, the "flap-let" will end up flush with the liner.

With rear flaps, the biggest problem is making the flap mate properly with the bottom quarter panel valence. Again, a little creative bending and heating will leave it perfectly flush. Note that the top of the rear flap is held on with a rivet. I always drill out the rivet and replace it with a sheet metal screw.

The sandpaper and steel wool will remove scratches and curb rash.
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'88 244GL, '89 244GL, '90 244DL, '91 244, '92 244