I have a 1999 E300TD
The transmission was acting up, hard down-shifts and a real fast 2-3 up-shift...
I got some estimates...........THESE PEOPLE ARE CRAZY!!!
Any way ….. I drained it and pulled the pan to see for myself.
At 100,000 miles it was rather dirty and brown looking.
So I took a chance and renewed the fluid and filter.
So far so good…..Smooth shifts and overall great operation.
I think that this is NOT “lifetime” fluid.
You know come to think of it ...the grrr sound could be caused by a cloged filter
The pump could be gasping for oil.!! The intake is a very small slot on the front-side of the filter.
And .....
Dont think for one minute that the S/Dealer is any better than an Indy.
There is lots of great Techs out ther that wont rip your eye sockets out....
Defiantly have it checked out. I know for sure your fluid is dirty.

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2003 SLK 230 (85000)
1999 E300 Turbo Diesel (388,000)
1991 350SD Turbo Diesel (185,000)