I have put 23K on my dually since I bought it. it came with 89K on the odo. I have been doing regular Oil changes plus fuel filters. I had been putting off doing the tranny service. Then I smelled that unmistakable odor of gear oil from the left rear, I couldn't see any leaks or seeps but the nose knows. Into the shop it went for a full going over. I had set it up for a full tranny and transfer case fluid and filter change plus look for the axle leak and check everything else. Transmission / transfer fluid was coffee black, whoops. front axle seals and bearings were good as were the pads and brakes. they changed the axle/ differential lube. Rear left axle seal was leaking, pads and rotors were under 2mm thick, bearings were still good. replaced both axle seals, Pads and rotors, flushed the brake fluid front and rear, bled the system, refilled the axle /differential. in and out in 6 hours total bill $1030, peace of mind sending the wife down the road with the camper in the bed towing the horse trailer, priceless