Do you have any specifics as to the cars involved / trans type and the original - 2nd failure?

A trans rebuild is not a new transmission, in most rebuilds 90% of the parts are reused, that is why it is called a rebuild. Failed and common to fail parts are replaced but parts that are still good are not. No one is going to x ray every part to see if it is soon to crack, no one can predict exactly when a part will fail in the future.

Another issue is that as the trans wears, internal leaks occur changing the operation of the trans. For example, as the valve body wears operation changes. For specific failures there are repair kits but it takes time for these fixes to come to market.

Also trans rebuilds are price sensitive, a customer just isn't going to spend 50% of the value of the car. As others have said, a Mercedes reman is going to be very expensive and I bet you wont buy one for a car with 300,000 miles + .

To give you some sense of numbers, I recently bought a 99 Blazer with a bad trans. The owner was quoted $ 1,800 for a basic rebuild , more if it had lots of failed hard parts ( shafts, gears and such ) The vehicle was in excellent condition with a street value ,if running, of $ 4,000 , they bailed on the fix.

I did a rebuild a couple of levels higher than basic retail. In addition to replacing the usual failed frictions,bushings and torque converter that the $ 1,800 rebuild would get, I replaced all bushings, all frictions and steel plates, pump vanes, all solenoids, internal wiring harness, case plug, both speed sensors, pressure sensor and rebushed a valve in the valve body.

Given I do consulting work for a trans shop, the parts were sold to me at cost, this pile of parts was $ 700 If the shop would have done this level of repair it would have easily hit $ 2,800, remember, this is a $ 4,000 car.

Telling the trans shop you are willing to pay for a premium repair _AND NOT CRY ABOUT THE PRICE WHEN FINISHED_ is a good idea if you are truly looking to keep the car long term.

In any event, please update this thread with what you have decided to do and include prices.