[RedRooster]

Do you see that number that says tech manual TM9-2330-251-14P, Do a search for military tech manuals and see if you can come up with one. It will tell you the part number and how to service the trailer.
I just happen to be a defense contractor and have many tech manuals on CD ROM, but I think that one is older than my data. I will check it out.
Once you find the part number you can search military surplus or Governmentliquidation.com to find the parts.

 

[RedRooster]

I don't have that one. The closest one I have is for an M332 which is a 1-1/2 ton ammo trailer. They are very similar and may have the same braking system. PM me with your e-mail if you want a PDF file of the M332 tech manual.
Once you find the part number you need, let me know and I can give you some pointers on where to find one.
Old military stuff is cool, but I can't help but think you could find some seals and rebuild the old one a lot easier.

 

[RedRooster]

You've got mail.

 

[RedRooster]

Yep. I forgot about the Logsa site.
It looks like the part number for the master is 10614. A quick search of my FedLog program revealed that the master was either made or sold by Tiger Line Equipment in Minster, Ohio. Phone 419-628-3388.
I called and spoke to a man named John and he said they actually still have some in stock. They are priced at $119. That's high, very high. If your friend wants to go back all original then they will probably be the only ones to have it in stock besides the other surplus place I PM'd you about.
Pretty resourceful group lurking in here, huh.