[Lynn Eades]

You are right. It is brand specific. Most oil companies produce a std mineral oil range, and a heavy duty range. Often the heavy duty range carries additives that attack bronze, and aluminium. These oils are for where there is a high tooth face pressure, as well as a high sliding situation, as in a hypoid diff.
Pedr, what did you end up using?. I was wrong about the EP oil,in the Dodge box. It should have a straight mineral oil, as there is a bush inside the reverse idler,that might be damaged.