Before the tranny flush is done, my friend wants me to run conditioner in the ATF? I know not to do that with the engine oil, but what about the tranny? How will the seals be affected?

 

Wow. This may start an argument as big as Chevy versus Ford! The best I can say is, it will do no harm. Just my opinion, but I've never seen any conditioner that did any good on a transmission. By the time a tranny is showing issues, it is too late for a can of anything to fix it. Furthermore, it would seem to me it would come right out with the flush. This is just my 2 cents, but I think most all of it is snake oil. About the only brand of additives I've ever used and occasionally had any perceptable improvements is the Lucas line...and I don't know that I've ever used Lucas in a transmission. Mind you, this is just one person speaking. You may have all sorts of folks beg to disagree and say I'm way off base.