Tomos company literature says (in different places) A and F. I found Type A in the local grocery store here, $2 for a quart. Heeters has Golden Spectro 80 wt 2-cycle gear oil, which is supposed to work very well, at about $6.50 per quart. Dexron Mercon is reported by reputable sources to shorten the life of the clutch lining. Type F is supposed to give a more pronounced shift feel, Type A gives a more smooth shift. The difference is additives that modify the viscosity under conditions of fluid shear (what happens in the film between the clutch drum and the clutch inner segments). There was a lot of posts about this not too long ago.