1986 Chevy Silverado

1986 Chevy Silverado

An auto repairman has tried to fix my truck. Two days after I drive it home all of the transmission fluid runs out on the driveway again. I think it is called a D tent (?) Cable that goes from the carburetor to the transmission. He replaces the little part that looks like a top hat with a hole in the top and gasket where it goes into the transmission. It isn't even being driven and the fluid runs out again, for the third time. What can be causing this to happen? Regretfully, I have decided to sell "Ole Blue" after all these years, but I need to get it fixed first. Any ideas would be greatly appreciated.