Is this definitely a window regulator problem?

[Multibeemer]

I have multiple problems with our 03 E53 that I'm trying to tackle. One of them is a front passenger side window that has all the symptoms of a regulator problem - it goes down easily, but moves up very slowly, and can't make it all the way up without assistance. About two years ago, my wife noticed these symptioms, so I took the panel off, and found the classical regulator problem, in that the plastic clips that attach the regulator to the window had broken. The rest of the regulator appeared to be in good shape, so I secured the ends of the regulator to the metal piece that attaches to the glass with a pair of zip ties, and it has worked fine ever since. Until now, that is.

So, I took the panel off, and my fix is holding - there's no sign of the regulator cable ends tying to work their way free. Also, the cables are where they belong - none have worked their way free of their pulley wheels, and nothing is binding up anywhere. In summary, the regulator visually looks perfect. So, could the problem still be the regulator, or could it be something else? If so, what should I check for? I don't want to throw parts at this thing until I'm pretty sure I'm replacing the right component. Thanks.