Leaky "Banjo" Fitting

[mercedesny]

Did a search and couldn't find the info I need on these fittings. I'm new to the "euro" hardware, so perhaps you folks can educate me.

I have a 1981 300D and have a persistent leak on the transmission dipstick "banjo" fitting that screws into the oil pan. The transmission is a 4-bolt pan, 722.118. I have replaced the aluminum seal rings following a filter/fluid change and have a leak that leaves a small puddle on the driveway. You folks have any tricks for stopping leaks on these things? There were no rings on the fitting when I took it apart, but it leaked then also.

Any information is appreciated!