In my OPERATOR'S MANUAL & PART'S LIST for my 721D it says:
"For Gemini transmissions, use Mobil DTE18M (Grasshopper Part No. 345280 for 1 gallon container). For severe duty, use Grasshopper Fluid Part No. 345050 for 1 quart container.
You will find that the Grasshopper fluid is very expensive ~ $18-24 per qt or maybe as low as $70 to 95 per gallon depending on dealership. IIRC, the Mobil DTE18M has been replaced/superseded with Mobil DTE 10 Excel 100.
Do a search here on Mobil DTE18M & you'll find some thread(s) on that subject. The 100 Excel will run you ~ $100 for a 5 gal bucket, which should be good for ~ 2 fluid changes, ...depending.
But there are those that are going a different route with a _____68 ( can't remember at the moment, ) or ____26 (I think) I'll go back & try'n get you those make & numbers.