I have a leak on my 1984 300D transmission
It is on the passenger side at the line that connects the transmission to an area near the radiator.

When I unbolted the 19mm bolt i did not see any o-ring of any type on the other side. So i matched a small o-ring to fit on the Outer Dia of the bolt and squashed it in there, but that did not work.

Is there supposed to be an o-ring there?
What is the best way to fix it?

thanks,

almadroog_7

If I read this correctly, you are talking about the transmission cooler line? That banjo bolt connection uses a crushable aluminum washer to seal the trans fluid there.
I would think any trans shop would have them, if not most parts stores.

I too have the same problem...how did you fix it?

these old trannies get leaky there cheif

I noticed a slow leak at the same spot on mine. I tightened down the banjo fitting to correct it but it made it much worse-as I tightened it a bit if o-ring sheared out from behind it. these fittings are supposed to have two aluminum crush washers-I got mine from the dealership at no charge. The lines are under reasonably high pressure and temp and an oring is not appropriate here. When I removed the fitting I discovered that the PO had used a combination of rubber washers and copper crush washers to try and compensate for a small crack in the transmission where the washer seals-bad idea for the crush washers to work the rubber washers will be over torqued and they only where sealing on one side!. I had to disconnect the exhaust to get good access, remove the retaining bolt on the metal trans line in order to move it out of the way, degrease the whole area with simple green and a tooth brush and grind a groove out along the crack and then repaire with JB weld, let it set for several days scrape the sealing surface on the trans with a soft plastic scraper(carved up bic pen) so as not to scratch the survace and the reinstall hollow bolt and banjo fitting with two aluminum washers, one between the banjo fitting and the trans, and another between the banjo and the head of the bolt. I couldn't find a torque value for the bolt so I tightened loosely, ran the car and then torqued it until there was no more leaking fluid. make sure to lube the bolt with ATF before reinstalling it. Worked for me, good luck with it.

sounds like you got creative over there. I personally quit working on cars, it was a hobby that i tried but i got too frustrated.