One piece windows - difficult to roll up and down

[stingray72]

The PO put single windows on my 70 and they're a real PITA to roll up and down. I have to grab the back of the window to keep it straight and it's still not easy. Being that I've never even looked at windows or the system before, what should I look for when trying to diagnose the problem? I've got to take my door panel off to replace the locking mechanism so I thought I'd look into this also