Originally Posted by 85MB300D

I can't comment on personal experience with synthetic ATF. I was told a few years back NOT to use it in older high mileage transmissions because, like syn motor oil it will clean so good that it will clean varnish/deposits off of the clutches/internals thereby increasing the tolerances and actually make the transmission SLIP and not work correctly.
Again, no personal experience on this, but it makes sense. I didn't want to risk it, so I went with conventional in my old 300TE w/ 237,000.

If anyone wants to offer any other opinions, fire away. Just what I was told.