I'll tell you about what ATF I use for my vehicles. I use WS in my 2008 Toyota Sienna. It has over 375,000 miles and I have it changed every 50,000 miles. It is the original transmission and engine. I also have 4 Mercedes that I use Amsoil Transmission fluid in them. The 1983 240D has a manual tranny and now has 70,000 miles on the Amsoil and I'm going to change it every 100,000 miles. The 240D has over 327,000 miles and still shifts just great. My 1984 300SD has over 258,000 miles on it and over 30,000 miles on Amsoil ATF fluid and I'll change it out every 75,000 miles. Of course it runs and shifts just fine. My 1988 E300 gas car has over 280,000 miles on it and over 50,000 miles on the Amsoil ATF and when it shifts it is almost imperceptible!! Amsoil ATF at it's finest!! My 1995 E300d has over 173,000 miles and over 23,000 miles on the Amsoil ATF. And, as I'm sure you would imagine, it shifts very smoothly as well. I will change out the ATF every 75,000 miles on my 124's. WS didn't work out so well for you and you went with a great ATF. I also like the Amsoil ATF. The WS worked out very well for me. If it would not have done so, I would have went with the Amsoil ATF as well.
Wow, extremely helpful! Thank you! Honestly, I'm more impressed with the Merc trannies lasting that long. Toyota is known for making stuff that will last forever, even if poorly maintained (didn't Scotty have a 'yota in @ 100k with factory motor oil that was still in decent shape?). Their mechanical engineering and build quality is that good. You could probably run these trannies on canola oil and they'd last 300k.
But those kind of numbers are pretty incredible for Merc, especially consistently across several Mercs. I know it's not unheard of, but pretty **** rare. I would say this speaks more highly of Amsoil than WS. Not that it speaks poorly of WS, just that the performance of Amsoil seems exceptional.