I have OE System cases on my recently acquired 87 K75. One of the System case lids has some light scratches on it from a driveway drop by the Prior owner.

The finish on these system case lids is much smoother than on my prior Oilhead and K1200 bikes,.....thinking that they might clean up with some wet sanding,....but thought I should check here first to see if this has been tried or if there is a tried and true method for cleaning up these case lids.

Brian in Austin

The plastic they are made from tends to get a bit furry when you sand it even with very fine paper.
I presume they are just black so whai I did may work.
Motospray here make rattle cans of paint specially for that type of plastic. I started with a quick sand and rub over with prepsol to get rid of most of the silicone and wax then used the Motospray clear prep coat then when dry the top black coat without any sanding and it came up tops.
You may have to hunt around if you dont have motospray brand there but I am sure someone will have the same product under their own brand.
I redid my tatty old givi cases and topbox and they came up really good, I actually had a mate say did you finally get rid of the old ones I bet the new ones cost a fortune. When you inspect it closely it can be seen to be the old ones.