The 1987 Sport Coupe uses a polypropylene skirt under the front of the car.
(I’m guessing at the specific plastic from the way it feels, and it’s response to abrasion, and heat. At any rate it is a Thermo Forming plastic. I imagine it could be LDPE as well. [Low Density PolyEthylene.])
Two things happen to the skirt. It gets torn, or it deforms. A torn skirt is difficult to repair. I’ve yet to find an adhesive that is flexible enough to work on a polypropylene for any length of time. They are all either to stiff and crack apart with a good whack, or they just don’t stick in the first place. My feeling is that only thermal, or ultrasonic, welding will hold a tear together like it wasn’t there. (Solvent welding doesn’t seem to work either.)
A deformed skirt on the other hand can be reworked with the CAREFULL application of heat. The trick it to heat an area without blistering, or melting it.
WARNING: Thermo Form plastics like polypropylene, and polyethylene can hold a tremendous amount of heat for a long time! DO NOT touch the area you where heating without good gloves! Do Not touch the front of the work or you may leave irreversible marks on it.
You MUST support the ENTIRE skirt while working on it. If you don’t you could end up with a sudden collapse that will ruin the skirt completely.
You want to heat the area you need to form evenly, and most of the time from the BACK side of the work. (If you heat the front you’ll make scuffs look worse.
Direct heat will open any scratches.) You can use a heat gun, or a propane torch with a big tip, and preferably a flame spreader. Work carefully and keep the heat source in constant motion. If you use a torch use a very low setting.
DO NOT use MAPP, Oxy/MAPP, Oxy/Propane, or any other metal welding/cutting torch.
Try practicing on the lids of some takeout soup containers. They have very close to the same properties as the skirt, even if they are thinner. (soup lids are LDPE, the containers are HDPE.)