Trans line leak at cooler line banjo fitting
 

During the installation of Eng and Trans in my 1980 300D I needed
to attach cooler lines (2 pieces) and 1 Trans fluid dipstick tube,
to the transmission at bottom of trans just behind bellhousing.

These are banjo fittings and I installed an aluminum washer on top and bottom
of each fitting and snugged them up. Did not see a torque setting
for these, used my judgement.

I have no leak at the dipstick tube, but I do have a leak (drip,drip leak,
not a fast leak) at the trans cooler lines.

I was careful to have clean surfaces and washers, clean bolts and threads.
Still I get a leak, the mating surfaces appear smooth and undamaged too.

So, if anyone has had this particular problem, do you have any advice on
this ? I hate to leave a leak on the car, so I will probably end up removing
the fittings and cleaning it all up and just doing it over.

Thanks folks.

you have the right idea. They do need to be a little tighter than you might be used to with respect to threads in aluminum.

I replaced the hard cooler lines on mine a while back. The dealer service mgr. looked it up as 35 ft/lbs. Make sure there are absolutely no burrs as they will cause leaks.(Don't ask me how I know.)

Also, the fluid tends to migrate along the line so a leak further forward, such as a worn area at a clamp or flex line, can be deceiving.