We just bought a 08 yukon denali XL1500 6.2 with 125,000 miles for $15k. I know that was high but it has complete verifiable service records since new and one owner. Traded our 03 tahoe as a down and never looked back!!!! These vehicles are the equivalent of limos imo, just finished a 1500 mile road trip and love the vehicle. i wouldent be scared of a rear diff seal, but these vehicles are excessively loaded with accessories that will "glitch" or fail. Ours is also not a daily driver, we will tow our 4k lb travel trailer with it and be much more comfortable/safe while doing it. Did your friend use it to tow? just be cautious with any vehicle with a primary purpose of towing.