727 transmission fluid question

The warranty is 3 year 50000 mile. I called and talked to the owner and he apoligized for some of his guys getting over eager to push the expensive stuff they sell in shop and ask the name of who told me I needed to buy one of those for a 727. He said he would honor the warranty as long I don't try to run heavy gear of or deer blood in the transmission lol.
He actually told me he likes to run Valvoline max life Dex/Merc synthetic because to flows well in low temperatures we get in winter and is cheaper than the others.