Just picked up a close to mint 04' GX. Truck has 120K miles and looks new and had timing belt and W/P replaced by Lexus 700 miles ago. Took her in for PA inspection a few days ago to a shop that I trust. Got the call yesterday that the 3rd brake light in the spoiler needed to be replaced. The prior owner promised to pay for anything needed to pass inspection. My shop quoted me $280 for the light. I felt bad passing that onto the prior owner as he gave me a good deal. I asked the shop to put it back together and I would pick up. I was surprised that LEDs would fail and thought it could be an easy fix and maybe the shop just assumed it was a bad fixture.
Popped out the light fixture and saw that the wire connecters were sitting in a pool of water in the spoiler. I took out the fixture and bench tested it and sure enough it worked. Went back the truck to search out the issue. Turned out that a wire into the connector in the spoiler had come out of the connector. Easy fix and saved $280. Just wanted to post this as I imagine others may have this issue if water is getting into the spoiler.

 

Like others have said, dealers and many shops skip the diagnostics parts and just want to replace stuff.
Why is there water in the spoiler?