This is for my BMW, but its pretty much the same as a MB, I think.
Autotrans (ZF, electronic) has 80K on it.
Drive it, after 10 minutes, trans dash light goes on and it goes into limp home (stays in third). Will stay that way all day. After parked overnight, it clears itself, and shifts fine for another 10 mins, and then repeats.
Dealer read the fault code, said it was an internal electrical problem. Either the valve body or the internal valve body harness.
Took to a trans shop, we disconnected the electrical at the trans and hooked up a manual shifting box. That basically bypasses the car's electrical system. Could not get it to shift. Confirmed that the problem is internal.
Now, I can get a rebuilt valve body and harness for $500, installed for another 100. But, there would be no guarantee on the results. And, the rest of the trans (clutches, etc.) still have 80K on them.
Or, I can get a whole rebuilt trans installed for $1700. Guaranteed for 2 years.
Any thoughts on getting just the valve body? $600 is much better than $1700, but if it makes more sense to just replace the whole trans, I guess I would do it.
Any advice appreciated!

If the diagnosis is correct then the VB is a good repair. The more common problem in BMWs is the harness, which is not that expensive. Unfortunately there are a number of other causes for the "limp home" condition including both internal problems and external electrical.

If your problem is external electrical the new tranny won't help. I wrote an article on BMW trannies. It probaly won't help but if you are interested it can be viewed at:

http://www.babcox.com/editorial/ic/ic100076.htm