Avoid is a strong word. The ones with the greatest potential for repair expense include:

- 90-91 350SD/L, 92-93 300SD and to a lesser extent 94-95 S350. All have the 3.5l OM603 which is frequently called the rod bender. Cars with engines rebuilt or replaced by MB have a very low incidence of recurring problems. If the car comes with documentation of a factory backed engine rebuild or replacement, it's worth considering. There's no way to check if an engine has bent rods without taking the engine apart. If it has the original untouched engine, it could go at any time. Typically the problem arises before 100K miles but I wouldn't put faith in a high miles original engine. Figure $10K to replace the engine. The 92-95 cars also have iffy AC evaporator cores which take 15-20 hours to replace. Figure $3000 to replace the AC evaporator. Other body systems like door closing assist can require time to troubleshoot and factory parts are expensive.

- 86-87 300SDL, 87 300D/TD. All have the 3.0l 603 in which the original head casting is prone to irrepairable cracks if overheated. The main observable symptom is cooling system pressure hours after the engine is shut off. There's no way to check if cracks are propagating in the cylinder head without taking the head to a machine shop for inspection. If you see one diagnosed to need a head gasket, chances are it needs a new cylinder head. If you find one with no symptoms of needing a new head, it can go a long time or forever without needing a new head. Figure $3K to replace the head with a later casting not prone to cracking - basically the 3.5l head.

- 90-93 300D 2.5. The original timing chain is prone to snapping. Depending on the operating conditions when the chain snaps, the engine could need a new chain or new valves, pistons and other things. If the engine is running well and there's no documentation that the chain was replaced, figure on $500 to replace the chain. Do it ASAP. The 190D 2.5 turbo which has the same engine is somehow immune to timing chain problems.

Other aspects to consider in the following models:

- 77-83 240D. It's very unfair that I list this car because it's bulletproof and childishly simple to service. The only reason I mention it here is that you have to develop an understanding of its abilities to drive it in modern traffic. I have some behavioral issues that won't allow me to be happy driving a 240D but based on the number still running, many people are well suited to it.

- 77-81 300D/CD, 79-80 300TD. These cars are only a little more complex than the 240D. The 5th cylinder makes them that much more difficult to service but you have to be as picky as Larry Bible to care The bigger engine gives them decent performance but the early type automatic climate control system can be expensive to service.

- 81-85 300SD. It is not my personal belief but some feel that the bigger body style and its additional ammenities means there are more things to go wrong than with a similar vintage 300D. I don't agree with this one bit. It has features like power seats which rarely need more than cleaning switches. If anything the bigger body means it's easier to service the engine and transmission which to me more than offsets the possibility of other failures.

I'm not familiar with the 190D so I can't comment on it.

Beyond these cars there's the 95 E300, 96-97 E300 and 98-99 E300 turbo. All share the basic 4-valve engine. The 95 has the W124 300E body style, the 96-99 have the W210 E320 body style. These engines seem to have an appetite for glow plugs. The glow plugs aren't difficult to service but more than a few glow plugs snap during removal requiring considerable effort to repair. Some early W210s suffer from front suspension mount points that succomb to corrosion and collapse. I don't know what it takes to repair the chassis but typically they are repaired if the collapse didn't send the car into a ditch or barrier.

Sixto