Deanna,

Replace them both. Forum's choice of rebuilt axles come from CVJ in denver, $300 shipped to your door for the pair. Costs another $50 in parts to do a complete job right. That includes the seals in the diff, washers, new sealant for the diff cover etc.

Jeremy4858 has an excellent thread concerning this some time ago that I followed. The FSM article is great for this job as well. Took me about 8 hours over three days, and I was a real newbie at that point and going oh so slowly.

Good luck,
dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car