Transmission advice or Anyone have an extra trans they want to get rid of...

[mike]

Hi
I'm brand new to d24t.
I used to have an 85 740GLE TD and drove it 82,000 in two years.
It was a great car.
I just bought another. An 84 760GLE TD.
Here's the problem.
I towed it home, in neutral, with the rear wheels on the ground and shortly after I got it home with only a total of 124000 documented miles, the trans is failing significantly.
At first it drives fine but as it warms up, it starts to lose the top gear then the next and so on.
After it is cold, it's good again until it warms up.
Do I need to do a complete rebuild?
Does anyone have a good used trans?
How many miles can I expect to get out of a ZF Transmission?
Thanks for the advice
Mike