I have a very slow oil leak at the front of my 1999 E300 (115k mi) recently. While the car was getting a 10k service I was advised that the leak is at a junction between a steel pipe and the aluminum oil cooler and the connection cannot be taken apart due to seizing of some sort, perhaps the result of joining dissimilar materials. Instead of what sounds to me like a simple hardware/plumbing job the solution advanced by the MB dealer is to replace both the cooler and the line in question, with the parts running somewhere in the $750 or so range, and around $1,100 including labor. Parts are now ordered from Germany. Does this sound "right"? (Sounds opportunistic to me)
Exactly how the leak is occuring is unclear (the "seized" connection is leaking; the steel pipe is cracked; the oil cooler is cracked; etc.). I'm not sure where the oil cooler is located so I can't pin it down.

Joe McGuire

 

With any leaks it is best to clean everthing and determine exactly where and what is leaking.

I have a older model (84 300D) but when I went to change the Oil Cooler Hoses I indeed did strip 3 threads off of the Oil Cooler Nipple (Aluminum). Apiece of the Oil Cooler Nipple threads stuck to the Steel Nut on the Hose and acted as a cutter to bugger up the threads.

On the older models there is a repair for the stripped Nipple. I do not know if that is so for the newer models.

It sounds to me like your Mechanic took the easy way out. If you do not do the job you cannot get blamed if the Nipple strips.
On the other end of this if there is no Oil Cooler Nipple repair for the newer models if he had done the job and the Nipple stripped you would have no Car to drive while you wait for the parts to arrive.

One of the members on another Forum recommended that the way to keep the Nipples from stripping when you are changing the hose is to use a small Dremel Tool with a Cutoff Wheel and cut a slot through the length of the Oil Cooler Hose nut and spread the Nut appart (or cut another slot on the other side).

If you happen to nick the Oil Cooler Nipple Threads by going a little deep it is not a problem because the Oil Cooler does not seal on the threaded area.

There might be another way to cut the slot but a chepie Dremel type Tool is around $25-$30. (I have 3 of them, one in bad shape 1 to replace that one and I bought another because it was on sale and it had a bunch of accessores with it. Ounce you have one you find uses for it.)

A regular Pneumatic Die Grinder (cheap) with a cutoff wheel could also be used but I beleve the Oil Cooler would have to be pulled out of the car (the Rubber part of the Hose could be cut) because of not enough room to use it in.