Non ATF+4 in a A500 trans..?

The electronic controlled transmissions that require ATF+4 should ONLY use ATF+4 or an acceptable substitute that is designed to cover the requirement.

From research and the what I personally have seen, because of the way the engagement of the TC clutch is done, which is by having slippage to allow a smoother engagement. Because of this intentional design of this operation, the friction of the TC clutch (and probably the other clutches as well) causes your standard Dex/Merc fluid to get hot enough to boil. When ATF boils it makes foam and that will cause all the clutches in the transmission to fry, and you might even see the fluid volcano out of the dipstick tube.

I'm sure using a little bit of dexron ATF won't hurt if you just need to get going and it's not long term.