This is all based around wear and tear of all the sliding components, the bailey channels and the white nylon sliders in the glass channels.
They were all perfect from new without cutting extra slots so one has to look and see what's worn down to give extra clearance and thus have the front of the glass hang downwards.
The answer is all the friction parts.
Disagree, it's the crap quality reproduction regulator assemblies.
We had a VS sedan we owned from new. The drivers window reg failed in 2014 so I had to buy an aftermarket unit.
Fitted without any modifications the window had no hope of aligning in the opening.
I think I ended up slotting one of the guide rail bolt holes about 20mm to get the window to fit right.
Unfortunately the stress on the crap quality reg broke some spot welds so I bought a different brand reg from All Crash Parts.
This one was better quality and aligned the window in the frame better. Still not as good as the OEM reg but OK.