Great Link
Dittio Gil
There is the do-it-yourself. Some avionics don't have a face plate and are all plastic like the collins tdr950 transponder.
I have refreshed some avionic face plates. Sometimes just a good cleaning with q-tips and mild soap solution is all that was needed. There are auto cleaning, shine, protective products for plastic, which can rejuvenate the finish. Be careful with silicone products and getting it on contacts. Not sure what's in some of these Auto products, but if silicon gets on bare metal you want to paint later, it can be heck to get off and ruin a paint job. In worse cases I have painted face plates. I went over it with a small brush and Testor's model paint (silver) and painted the trim. I supose you could paint the whole face plate if you can disassemble it.
Cracks can even be repaired. One way is with a soldering iron and getting some ABS plastic from a hobby store. You literally weld it back together with melting it and fill it in with the plastic, going back, sanding and buffing. The simple way is epoxy glue but that leaves a line.