Going to change all the fluids for the summer and was wondering, should I use synthetic or regular fluid in the transmission. Is it like oil, where you should only use it if the car is new or you may have leak issues? Just curious on peoples thoughts. Any input is greatly appreciated. Thanks in advance.

I haven't yet switched either of the Benzes to synthetic ATF but will be doing so at the next scheduled service. I have read on the Ritter/Easley list that it works out well, especially in cold weather areas where trans performance is compromised until the fluid is warm. I used synthetics (both Redline and Mobil 1) extensively when I used to live in Colorado and noticed significant improvement, especially during sub-zero start-ups in the high country, but better shifting in warm weather too. In fact, Redline 75-90 transformed a manual trans in an Audi quattro from being a candidate for replacement to quiet, smooth and slick shifting. Redline MTL is what the BMW guys use to get their cars' manual transmissions to shift as they should.

I've converted all of my MBZs to Redline synthetic trans fluid...converted the '88 TE in '96 at 68k, and the '92 500E in 1999 at 43k. No leaks, excellent performance so far. As of now, the TE has 170k and the 500 is up to 87k.

I had been using regular ATF for the past 13 years. so far, ..performance is still great. Drain and replace ATF including the torque converter every three years,..nothing change.

Like RUDY said if the frequency of change is regular then DINO fluids good enough!! BUT if you are seeking a bit of added protection & the cost being twice(at least) as much doesn't affect you, they go synthetic as IT'S really worth it. I've used nothing but synthetic fluids for over 10 years!

I just had my Auto trans in the 300CD flushed replaced the filter and fluid with Mobil 1 Synthetic ATF.

My first impression as soon as I drove off was that.. the shifting was very very smooth. Sure enough it's a weird transmission and I could pick out a shift or two that I can actually feel. However it's a lot smoother and I guess it's just keeping up with the maintenance.

It could've been the filter and fluid though. However the ATF looked pretty clean before the change even.