i have a 1993 xtra cab v6 4x4 with 217,000 miles. I off road regularly with it. My rear diff started leaking before and i found out the bolts were sightly loose. But now the diff has started leaking again, and tightening the bolts won't stop the leak. What should i do? should i change the seal... will it be difficult to change the seal? what are the procedures?