I will be the contrarian. I would only fix it if it is less then $300 total otherwise dump the car. Old MBZ is bottomless money pit. Salvage some useful parts then part it out. There is a lot of car in the $2500 range. You drop an engine in then somewhere else will break, then back to square one.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I would disagree, at least at a $2500. You can find a lot of cars in that range but every single car I have looked at or bought in that price range has needed lots of suspension bits replaced plus a litany of other work. I'd say if his in good shape otherwise, both in a mechanical and cosmetic sense, he should fix it or he'll waste a lot more time and money on the new car than this one. It sounds like this one is otherwise well-sorted, it's had it's suspension redone, repainted, window seals, etc. If this one has rust then yeah, it's junk, but otherwise it's better to stick with a car you know than one you don't know. He'd do better looking at cars closer to $5k, they'd probably need a lot less work than something at $2500.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.