Behind the neutral saftey switch there is a quarter size plug which looks like a freeze plug. Mine started leaking 1 month ago. Normaly the tranny needs to be pulled & dis-assmebled to replace the O ring which is behind the plug.
There is no pressure behind plug.
What I did was remove neutral saftey switch. Cleaned the area with Acetone,. Then I roughed up the plug with sandpaper & the raised area which surrounds plug and tranny case also. Cleaned area again with acetone.
Using JB Weld , coat plug and surrounding area unto case with a layer of JB Weld. Let it hardend enuff to get tacky.
Here is the important part: Take a nickel (5cent piece) lightly coat one side of it with JB Weld, then press it into the plug. It fits perfectly Then put another layer of JB Weld over nickle onto case. Let cure or harden for 16 hrs. Then drive.
I tried 3 times with 3 different epoxies. The JB Weld & Nickel is what worked.
3 weeks leak free.

BTW This was on 95 300E Diesel

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82 300 TD, 215K, 06 Dmax LBZ 245K,
2015 VW TDI Golf Wagon 70K

I like JB Weld.
Other Epoxy will work but you need to read the label concerning the Max temp the epoxy can take. Duro used to make a similar product.

I live in S CA and I have always been curious if it gets really cold if JB Weld will shrink?

I the Shop I used to work in we Rebuilt a Stanydyne Fuel Injection Pump (RoosaMaster) for a Guy for his Generator Engine that He had in Alaska. The rebuild Kit came with Nylon Pipe type Plugs.
In Alaska when the Generator was off it got cold and when the Engine was started the Fuel Injection Pump leaked from the Nylon Pipe Plug until it got warm.
Replacing it with a Metal one cured the problem.

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84 300D, 82 Volvo 244Gl Diesel

I am not sure it is going to hold. The reaction piston moves and will break the weld when the cavity is filled with ATF. Hope it works out for you.

You can change out the seal without dropping the tranny. It is doable but a lot of work and very little room. Been there done that.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

"I am not sure it is going to hold....."

Funny, Marriage is the same way

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Eric in Plano,Tx
85 300D 277K overall miles
65K on WVO (2 tank)
Rebuilt Transmission at 245k miles.

96 CE LT1
94 Nissian Hardbody
96 F250 XLT PowerStroke (also runs on WVO)