First you need to either find another dealer or someone you trust if you can't do this or any other maintenance on your car. He is taking you for a ride! From what I just read, this guy is just plain untrustworthy. Next, although I'm not familiar with your car, you are correct, without taking aprt the car it's hard to make a blanket statement like he did, although I will say, IF they have seen this type of problem before maybe that's why he did, but then again if they've seen this type of problem before he would or should have told you " Yes we've seen this before and this is what it is" That's from experience, which is what they have from working on these cars. Now as far as your problem, where is the seatbelt wet? Upper portion, lower portion, back top, lower bottom? Have you felt around the floor, is any of the carpet wet? This includes under the seat? Did this happen the other night when we had our first rain of the season? If not take a hose and with the doors shut,(obviously) start running water all the the door seams and all around the door, not for a minute but for a good couple of minutes, sometimes a problem like this takes a while before it shows itself. I'm right down the block in Tracy CA, if need be shoot me a jingle and we'll try and figure this out and save you some money. but definitely dump that dealer.