Bill H

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Here is a 1952 CHEVROLET car & truck SPECIFICATIONS (restoration pack)
Go to TRUCK SPECIFICATIONS 2nd column Universal Joints and Propeller Shafts, page 135
or go HERE Vehicle Information Kits scroll down to Chevrolet Trucks click on Show find your year and click. same page 135

Vehicle Information Kits
Restoration Packs
Resto Packs
Chevrolet Car & Truck Specifications sheets
All are the same thing and have the same information, some may be clearer than others depending on how they were scanned into the computer.

As far as your truck, if you have the same extension shaft, then you must have a long bed.
Chevs of the 40s has Torque Tube Ball Seal Kit For Drive Line. Manual Transmission. 3/4 ton truck.
You will have to tell them you have a long box and I
think you will need 2 sets.
Call Northwest Transmission Parts ask for John if he does not have it, he will tell you where to find it.
He might just have everything you need to stop the gear lube from leaking.

Q.Is this the same transmission that is in the 1/2 ton (3100) trucks?
A. Yes

If you can take some pictures of your leaking drive train and post them here it would help.
If you need help linking pictures go HERE
If you need help just ask.

Does your drive shaft stay enclosed (hidden) all the way to the axle housing?