I bought a new on for my Farmall H and it's lasted less than a year. These new ones are crap. The old one didn't leak but the shutoff valve was too stiff to turn. Is it possible to rebuild an original?

There isn't much to them, the gasket the bowl seals against and the valve. I can't recall what the valve was made like. You might have to adapt a new valve to the old casting.

They used to sell new cork gaskets for the sediment bowls on a C Allis Chalmers.........but it was over 25 years ago since I bought one.

You can buy cork sheets at Ace hardware and some auto parts store.

Usually the valve has a nut that locks it in. Unscrew it and then screw the valve seat out.There is probably a packing or 0-ring on it that can be replaced. A good soaking in Kroil or Break Free just might clean it up to make it easier to turn.

Most of them leak because the threads strip out on the nut on the bottom of the bale that holds the bowl on

Here are few that Amazon carries.

https://www.amazon.com/s?k=gasoline+sediment+bowl&crid=12F6IMVZ7FNH0&sprefix=gasoline+sediment%2Caps%2C189&ref=nb_sb_ss_i_1_17

I'm sure you can get just the valve...