Cab Ventilation clogged

99 W900 had the 1 piece curved windshield replaced a while back and the windshield keeps popping out of the glue seal, had the windshield re done twice and noticed it is loose again, told a mechanic and he stated the cab vents must be clogged, it makes sense to me because when i close the door with the windows up i notice the windshield pops out, the cab has always been tight when i close the door.
Does anyone know where the cab vents are, he told me on the bottom of the cab but i can't find them.

 

The gasket on the one piece curved windshield is different then any type i have had replaced, it doesn't have a lip on both sides, the gasket is installed on the glass then glued onto the cab.
The mechanic wasn't the person that installed the windshield, i mentioned my issue to him thinking he might know of reputable person to set the windshield correctly, he stated that if the cab vents are clogged it would cause this issue and stated he has seen this issue before, i haven't seen him since, he told me the vents are under the cab but i can't find them.
The cab is very tight, most times i crack the window on the drivers side to close the door, if i don't the door doesn't close all the way, i own the same year KW T800 that i purchased last year and the cab is nowhere near as tight as the W 900.

 

Did any of them have a one piece curved windshield, the gasket is different then the one piece flat, 2 piece curved and the 2 piece flat.

 

That was my idea because the gasket looked original, in hindsight i wish i didn't have them change it.

 

I don't know what urethane looks like but the material they used was black, the glass doesn't touch the glue, the rubber gasket is installed on the glass and the rubber gasket is glued to the cab.