Safe to put in Mercon V in A833?

The FSM calls for ATF, or gear oil, depending on the temperature. ATF in winter, gear oil in hot weather. I have run both without any negative side effects.

I do believe that the hypoid component in gear oil is better for the gears, particularly in hot and heavy loading applications (pulling a trailer in the summer).

Probably a good quality synthetic is the best option, the best of all worlds, but you need to have modern replacement syncro rings in it with the chanels cut. The synthetic is too slippery, and with the standard factory syncros will actually prevent them working and cause hard shifting. The chanels bleed lube out of the syncro.