'97 E420 with 90,000 miles. To change tranny fluid or not.
 

Never been replaced. Should I get it flushed or leave it alone? Tranny is fine. Plan to keep car one more year.

If you're definitely going to sell the car, you might not change the fluid. If you plan on keeping it, or there is a chance you will, then change it.

"Fill for life" translates to "fill for the life of a lease..."

I recently changed my 98 E320 with 80Kmiles trans fluid & filter. The fluid was filthy and there was a thin layer of sludge on the bottom of the transmission pan.

In my opinion it would be cheap insurance to change the trans fluid & filter. Make sure you use the MB approved synthetic trans fluid.

Read M.B.Doc's comments on changing the fluid on the transmissions on the SL500's, which also don't require fluid replacement by the factory:

http://www.peachparts.com/shopforum/tech-help/49296-sl500-need-advice-post286069.html#post286069