Not sure if we are talking about the same problem or not.
We had a problem with our shower door dragging from day one. Four different Montana dealers nor the Montana plant were ever able to correct the problem. Montana even went to the extent of replacing the entire enclosure without out correcting the problem.
I finally tired of others failures and decided to take on the problem on my own.
First of all I removed the Original self taping screw (see picture) from the metal wall channel the enclosure sets in. I than drilled a hole thru the enclosure and the wall channel stopping as soon as I was thru the channel. I than screwed in a 3 inch drywall screw (see Added 3" DW Screw). At this point I replaced the Original Self-taping Screw and the door has not dragged since and it has been at least 4 weeks.
Hopefully this will solve your problem as well.