I think the only possible risk might be to friction surfaces, like posi clutches, and I am not certain about that, Jeff. If you want positive confirmation you might consider giving Lucas a call and I suspect they will provide you the best guidance possible.
I am in the same camp as John (Grubby) with respect to synthetics in the diff. Someone once told me the synthetics would run cooler but I am not certain about that. I do know I have had three daily drivers I drove over 300K miles each, that did not use
synthetic in the diff and also did not have any problems.