Ive used tractor supply ATF Dex/merc and no problems at all (you can buy it for 30 dollars for 2 gallons). Change at 20,000 miles along with filter and you will be good with any D3 ATF.

Im running Brad Penn ATF-D III-H now. No specific change, feels like I did nothing. Some people use Mercon V in these transmissions and report extremely nice shifting.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)