I just had the tranny fluid replaced and a new filter put in on my '05 C230K. The car has 114,000 miles on it now.
When I mentioned the "lifetime" tranny fluid to my dealership service advisor, he said he had never heard of that.
He advised to change the fluid and filter since it's so hot here in Arizona and heat is the big killer of transmissions.
Changing the fluid is not in the service book that comes with the car, but I wanted to do it anyway. I fail to believe
anything is "lifetime" anymore. If nothing else, it might help save an expensive tranny repair later on if I keep the
car. So, I did it and asked to have them return the old filter in a zip lock bag so I could look at it to see not only the
crud that might be in the filter, but also the color and condition of some of the old fluid with that many miles on it.
I was surprised to see that there wasn't a lot of junk in the filter and the color of the fluid wasn't as bad as I had
thought it might be. I have seen a ton of transmissions drained and some of them looked horrible with a lot less miles
than I have, so.......I was pretty happy. I would also think about replacing the spark plugs at 100,000 miles. I did, and
it restored the performance back to when the car was new.

 

agreed. when i purchased my 05 C230K first thing i did was a tune up after a week.after 3 months i had tranny shifting kinda hard took it to dealer said it needed fluid change. and like you i heard from my last service a checkup that it was lifetime and was based like synchro mesh viscous fluids. even so i paid for the tranny service and it was night and day lots of winter and salt up here so filters get changed alot more in the city than the country. so location is a factor and your in heat and its well known that heat is our enemy when it comes to internal combustion engines and its related components.