Check the owner's manual...
for an approved substitute oil. Most likely Dextron or Mercon oil. Automatic transmission fluid is a hydraulic fluid, and they have good detergents in them which I think is a good thing in older equipment. I changed my 1999 Rayco 1625 fluid with Dextron (III?) which was an approved oil by Rayco. If you do not have an owner's manual, you can usually get them from the manufactor or via .pdf. Good knowledge to have. And on the last note, there is a difference in oils, just use something that crosses over into an approved oil by Vermeer.
Good Luck!
Bob