I don't want to start a war here but what brand ATF do you use and why? In my 518 i used Pennzoil and it always seemed fine. Is the higher end stuff (Amsoil, royalpurple etc.) really that much better? I don't tow often maybe 8-10 times a year.

 

For a 518, synthetic should lower your temps a few degrees. Other than that, the Pennzoil ATF works just fine. Been using it for several years.

 

I've been running amsoil just because that was the only synthetic I could find at the time. I've had good luck so far and I tow a couple times a month.

 

Any ATF that meets spec will be fine for your use.