What series transmission is it? I may have a service manual that covers it. From what I see in my manual, the body of that block is held in place by the hex nut. Inside, there appears to be 1 or 2 more O-rings to seal the block to the transmission.

Thanks very much. It sounds like I can remove that hex nut and check without opening a can of worms. That block is actually secured by the overload switch itself. It's loose at that seam, and being held in place by the tubing.

It's a 722.3; The exact MD is 722353 03 538026. The parts counter guy said it looks like there was a mid-year change to the overload switch, which is probably why the one I purchased is wrong. But like I said, the switch doesn't look like it's the problem, and the O-ring wasn't it either.

I have a detailed diagram that shows everything but the block (that only came on some models). However, I don't know how to convert a PDF file to Jpeg so I can post it here for you.

It allows you to take a "Snapshot" of your active screen.
Then you use the "Attachments" to Browse to the Desktop and upload the
screen picture.

http://wisdom-soft.com/products/screenhunter_free.htm

Attached Thumbnails

 

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'84 300SD sold
124.128

Here is a link to the MB service manual: http://w124-zone.com/downloads/photos/300TE/remove_tranny/tranny_722_repair.pdf

Don, the section that you need is on page 91.

Is this the image you are talking about?



Looks like I have a weird one-off configuration. That's the same hole, right down to the notch through the threads, but it has a different kind of overload protector, underneath a plug, and the kickdown solenoid located in a completely different spot.

I've got this,

screwing in to this hole,

topped off by an electrical connector.








I guess at this point there's nothing for it but to dive in and see what's in there.

Thanks again for all the help.

Yes, that is the one. After looking at hundreds of different pictures and reviewing 5 different manuals trying to solve my own problems, I've learned that there are many different external accessories to our transmissions, but for the most part they are the same internally. I suspect that you'll find one of those O-rings inside is the culprit of your leak. Let us know what you find. That's how we learn from each other here. This site is a great resource with many experienced folks who are willing to share their knowledge.