w116 300sd ATF 722.1xx
 

Going to drain the ATF from my 300sd and would like to replace the ATF with Synthetic.

Is it a good idea to use Synthetic, Redline, Amsoil?

I want this transmission to last a long long time.

If Dextron ATF will give same results then I will stick with that and replace it a regular intervals

Please advise

In this forum there don't seem to be many people running synthetic transmission fluid in the older cars. In previous groups (mailing lists) that I belonged to, it was more common, mostly Mobil 1. Some claimed that it improved shift quality.

As far as I am aware, however, there is no hard evidence that running synthetic ATF will have any long-term benefit for the transmission.

Given the cost of doing a complete drain and refill (including the torque converter) using a quality synthetic, in the absence of strong evidence, I would stick with regular Dextron-compatible ATF.

I run synthetic motor oil, but run regular ATF.

I too don't believe there is any benefit to running synthetic in an old car. You are unlikely to drain out all the old fluid anyway.