On my 1991 300d, the fog light covers always look like they're fogged up from the inside; the plastic is not clear. Maybe that's the way they're supposed to be but seems like they would have been more clear than how opaque they are now.

Unless your headlight seals are leaking and the fogging you see is condensation, it's not the inside that get's fogged.

Road rash and yellowing plastic is what happens. The easiest way (that I use with amazing results) to bring back faded fog light covers or any plastic headlight for that matter, is to wet sand with 1000, then I'll use my buffer and hit them with rubbing compound. Seal it with wax and viola, new lights. There are headlight restoration kits you can buy at any McParts store to the same affect. My process is less than 10 minutes for both sides. Power tools for the win.

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Allen Kroliczek
Oak Grove Autosport | Oak Grove Autosport
01 G500, 82 300TD, quite a few more.....

I just had to replace a set, they developed a bad case of Odocoileus virginianus, they ran about 60 dollars a peice

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1993 MB 300D 245K died.

I've seen that stuff they sell on TV and never understood how they could make them like new from the OUTSIDE of the car. I was almost going to buy some of that stuff, when I read that toothpaste does just as well. It's slightly gritty and can basically sand down some of the opaque stuff off of the front of the plastic. I tried it but it didn't work. Mine might have some condensation behind them and maybe I do need something stronger to hit the fronts with, like the sandpaper you're talking about.