That could be good or bad. Luckily it sounds like this is the cool side of the oil. I'm not sure how hot the oil gets but you wouldn't want it melting through the JB Weld.

The Oil Cooler does not get hot enough to melt JB Weld.

I lost some threads when I backed off the Oil Cooler Nut. When I reinstalled the Nut I degreased everything with Brake Cleaner and applied JB weld to the Threads and the back inside if the Nut.

The read arrows in the Pic point to the excess JB Weld that is still on the out side. That JB Weld has never softened.

That was about 4 years ago.

I was wrong about the max temp; that is double.
This is for the normal JB Weld not the Fast cure one.

"How much heat can J-B Weld withstand?
Original J-B Weld can withstand a constant temperature of 500º F. The maximum temperature threshold is approximately 600º F for a short term (10 minutes). Refer to individual product packages for more temperature information."

Other stuff I did not know till I looked at the site. When cured it is non-toxic and it is Microwave Safe (this was surprising ).

FAQs » JB Weld

Sweet, does that mean I can use it to fill my cavities :D

You think you are making a Joke but for the last 20 Years I have had issues with My tooth Fillings. The silver colored Metal Amalgmum (this is spelled wrong but that is how it sounds) filling material does not hold up well for Me. I get about 2-3 years use before they fail.

That material used to have Mercury in it and I think when they changed it to be non-toxic it is not as strong as it was.

So when I saw the non-toxic that rang a Bell in My mind for use as a Filling Material.
Then as I read on I found in order for the original JB Weld to stick it has to be dry. That is difficult to do in your mouth.
The next issue is that when JB Weld gets warm (remember your body temp) it gets kind of runny so you would have trouble getting it to stay in Place.

So, I took a look at their Products and they have a Putty (water weld) that is for use wet and it dries white. That sounds ideal till I pulled the Material Data sheet and found that like unlike the Original Formula it has several toxic items in it.

If you are good at casting stuff it might be possible to make an impression of a Tooth and make up some Plaster Molds and make a casting (Silver?) and make Metal insert and use the Epoxy to hold the insert in.

The leak stopped after installing a gasket made out of relatively thick gasket material that I had. I cut it so the hole matched the pipe and the outside circumference was a tight fit into the nut.

I assembled then took it apart to examine. The gasket took the shape of the male hose and the hole was centered. I reinstalled and ran the engine for 10 minutes. No leak. I expect it to hold since the gasket material is normally used between 2 metal surfaces, frequently surrounding oil passages.

Comments?

If the Gasket Material was thick enough to get some good compression on it should be good for 3 or more Years.
If it leaks again you can just make another one.

Check the fitting on the cooler
 

I had almost exactly the same problem and it turned out the fitting on the cooler had a hairline crack that was almost invisible. When the oil cooler line was attached the crack expanded and leaked. he more I tightened it, the larger the leak became. If you start the car and tighten the fitting a bit and it causes the leak to get worse then that is your problem. A trip to the wrecking yard for a new cooler fixed it right up. I do have some of the repair fittings for the old cooler and one day will fix it up for a spare.

I think Id be giving teflon tape on the threads a shot before JB weld or the other suggestions.

The seal isn't the threads. It is the surface of the ball on the male end of the oil line against the female surface of the cooler.

Essentially gasket material between the normal sealing surfaces took care of it.

I think thinner copper would have sufficed also if heated and softened. The washers I had access to were to thick.

Have you noticed any 126s in yards around you? I need misc some parts.

The seal is similar to they way the Fuel Injection Lines seal at the Injectors and the Fuel Injection Pump.
Except that the Oil Cooler Hose Male ends are rounded instead of being cone shaped.

TRUCKTEC PARTS
 

I think your problem is in your first sentence....that you bot Trucktec oil cooler lines. I haven't done the repair you describe, but it isn't surprising that the lines aren't mating. Even though the lines came in a box that said Trucktec and Germany, Trucktec sources their parts in places like China & 3rd world countries and just puts the part in a box with their name on it & Germany with the implication it is made in Germany and thus of high quality. They are simply a re-boxer, not a manufacturer, and thus quality is usually very poor. Checkout Gerry VZ comments over on *********.com for a whole lengthy discussion on who makes good Mercedes parts and who doesn't. Those guys are all over the problem of inferior parts being sold at premium prices all under the guise of being Mercedes quality parts. They have a long list of manufactures that are good parts makers and those to be avoided. Trucktec is on the avoid list.