Nothing less than a FULL synthetic oil, be it Mobil 1 or Amsoil, or whatever you prefer and can easily obtain locally. If the oil drain is not on the bottom of the pan, but rather on the side, you might consider a Fumoto drain, as it makes the oil change process very easy. You just dont want to install it if it will be hanging down where something on the road can shear it off.
Also use a full synthetic transmission fluid meeting the specs for the transmission. I prefer Amsoil, (In my Sprinter, I use a fluid approved by Mercedes however) It would be worth considering installing a deep aluminum pan on the transmission. You get a drain plug, a place for a temp probe for a trans temp gauge, and extra capacity to help keep it cool, plus an aluminum pan seems to dissipate heat better than a stamped steel one.
Charles
