I am not sure what was used originally in this Bolens differential box. The same differential was used on JD and some other brands 30 plus years ago. It is completely dry and seems like it is full of dry dirt and grit. Note all of debris on the floor which fell out of it. That pic was taken seconds after I opened it. After I clean it up, what king of grease would you recommend? All that is out there today was not available when this was made. But, Please be practical. The JD has grease fittings on it but on this Bolens , they took the cost savings and did not add any. I may add a grease fitting or two. Thanks.