4 grand is a bit much. I agree that the rough idle is probably eng mounts and possible worn engine shocks. Yes the engine has 2 shocks, they are about 10 inches tall and cost about $35 a piece. The rear "fog Light" is actually your reverse lights. You are talking about the lights under the bumper? A new lens might run you about $15. One thing to check for is the self leveling system. This is on all TDs. With about 2 people sitting in the back, and the engine running at high idle, the rear should raise to level. The system is pretty relible, the thing that goes usually is the air cells in back. There are 2 of them, one for each hydro-pneumatic shock. I paid $2900 for my TD and all I HAD to do was put some new tires on it and new belts. I of course changed all fluids and filters just to establish a base line. My TD still has it's original Becker "Europa" cassette/radio and it still works. Just a little FYI, for model year 1985, MB made only 3,713 turbo diesel Tds. They also retailed around $34-36,000. My TD in 1983 cost exactly $34,612.

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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