I have used GM Autotrack, Dex/Merc3 and Type F ATF fluids in my gasgas. I change it every 3-4 rides and never had a problem. Once you go with a fluid stick with it. Don't try experimenting between one versus the other because you will take out the clutch.
My fiance had been using some ELF eye of newt 38 euro a bottle stuff and it was nothing but problems. Went to good ole ATF with a new clutch pack and its working fine.
--Biff