I had an '88 'Burban that the sheet metal above both rear wheels rotted away. I discovered that when I replaced the rear speakers. That was an easy fix. My '99 'Burban leaks in the right rear and sometimes under my weathertech floor mat on the front passenger floor is covered in condensation and the carpet below is wet. Haven't found that cause yet. For the right rear, so far I've: had the right rear glass removed and reinstalled. My body shop guy laughed at me when I asked him to it, but he was shocked when he removed it and discovered about 22 inches of the top rear window seal was not sealed. That reduced the water infiltration, but didn't stop it. Next, I replaced the cargo door hinges (a really unpleasant ordeal, though the doors are nice & solid again), but it still leaked, just not as bad. Next, I replaced all of the rubber weatherstripping for the cargo doors 100%. It is now much better, but still leaks!?!?!?!?! When I'm parked, the front end is higher than the rear due to the incline in front of my house and other than the car wash, water doesn't get in there at all and even the car wash now may or may not add water. I pulled back the rear carpet up to the right rear wheel tub to see what I could see. At the rear of that tub there is some rust, telling me it's been wet for a while. Last time it rained hard, this area was wet. Metal above the wheels is solid so I am baffled where the water is getting now, though there are seems that could be leaking. Need to pressure-water-test them when it gets warmer and see if I can discover the access point. Very frustrating. Oh, one of the first places I looked for the leak was the roof rack and rear brake light assembly on the roof. No water getting in there, but I did manage to spin three of the blind nuts that the roof rack screws fasten into. Another fun repair to replace the blind nuts and I siliconed each fastener when I reassembled the roof rack and brake lights just as an extra measure of precaution. I love my truck but what a nuisance leaks are.