Looks like the paint on the old 300D is starting to show its age. Other that getting a new paint job, what would you recommend to preserve the paint and "restore" what's left of the original finish?

You have a couple of choices. One you could take it to a body shop and have them polish and wax the car for you. Of course they use high speed buffers that even a pro. could screw up and "burn" a spot in your paint. Two, you could spend a day and do this your self with some basic products from your local auto parts store. Of course all this depends on the present condition of the paint. Most wax companies these days have their own "1,2,3" system. Step 1 is to clean the paint with a polish. This will restore some of the lost luster. Step 2 is usually a glaze/sealer. This fills in any spider webbing that developes from washings and such. Depending on how much webbing your paint has, the more coats of glaze/sealer you'll need. The final step is to wax the car, preffably with carnuba wax. The most common waxes are Mothers(red cans and bottles) and Meguiars. If your paint is really bad off, you could start off with a polishing compound and then work your way up throught the 1,2,3 process. Using a orbit buffer will make it easier and faster. Always use terry cotton towels, ones that have not had fabric softener or dryer sheets used on them. These 2 products produce very fine streaking when buffing off the wax.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member