I just bought a '97 E420 and took it to two different mechanics locally. I asked these mechanics' opinions about several issues, one of which was the changing of the transmission fluid. The mechanic closest to my house says I shouldn't touch it and that it is good for the life of the car, but that if I did want it changed, could I please go to the dealership and pick him up a dipstick. The other mechanic just down the road insists on changing it every 30,000 miles, no less!

Lifetime? Every 30,000 miles? I need to buy my mechanic his tools? What's going on here? And the second guy went on to say that if I left it alone and didn't change the tranny fluid I could expect the thing to fail at 75-100,000 miles. I'm beginning to wonder which guy is worse. The ignoramus or the liar?

Is there a more definitive time-frame for a tranny fluid change? Assuming I stick with factory fluid type, what is the real answer to how often this fluid needs to be changed?