That is a pretty easy fix. Remove the driveshaft. Mark the pinion nut so you can set it back the same way it is now. Remove the pinion nut and pop out the seal. Replace the seal and tighten the nut back to the mark you scribed. Reinstall the driveshaft. Check and refill the diff if needed. You may want to check a service manual first or take it to someone. It shouldn't cost over $150 to have it done. Sometimes the pinion bearings wear out so check it carefully for play.
2006 Superior Blue Trailblazer SS AWD, Stock as a rock
Sold: 2002 GMC Sportside Denali front end with a 2002 LS1, FLT level 5, Yank 2600, Trick Turbo, T76, Nelson intercooler, 60LB injectors, Warbro fuel pump, Eaton locker, Magnaflow, 3.42, Nelson Performance Tuning (speed density).
Sold: 1981 GMC LB RC 1500 2002 4.8L 4L60E 12 bolt 3.73 Richmond Lock Right AC PS Nelson Performance tuning