You can use a variety of weights. The shop manual on page OB-8 and OB-9 has a usage chart.

As for the cleaner in the diff fluid that wouldn't happen from what you described. The axle is solid and there is no fluid that runs from the diff to the CVs. You may have had some seep into the housing from the breather tube, but I think that possibility would be remote at best.

Just my thoughts.