Question re: window regulator and mechanic's responsibility

[hes]

I have a 2000 Boxster that had problems with moisture coming in through driver's side door. My mechanic traced it to a rubber seal in the door that needed to be replaced. Not the vapor barrier; it's a rubber seal that goes around entire door, surprisingly expensive part. After I got the car back from installation of the rubber seal, the first time I tried to lower the window completely it stopped an inch or two from bottom of window opening (i.e., opened shy an inch of opening completely). I then tried to use switch to move window back up to close it, but it wouldn't move (or may have moved an inch or so, not sure).

At this point I'm thinking that the mechanic failed to adjust something properly when they put the door back together (I don't have clear idea of how electic window regulator/motor system works). But it was raining and I have no garage, so I tried jiggering window switch up and down to see if that would help anything. It didn't, I tried using my hand to help window up, that didn't help. There was grinding when I used switch, and at some point the grinding stopped, the motor was still whirring when I pressed the switch, so I figure I broke something. At this point the window moves freely up and down, so I lift it with my hands to closed position.

My mechanic now says it needs a new regulator, that it's common for regulators to go bad in Boxster with 75,000 miles, and that it is a total coincidence that I had this problem the first time I tried to lower the window after they worked on the innards of the door. This sounds odd to me.

My main question has to do with whether my initial problem with window (the stopping an inch or so from bottom of window opening the first time I try to open it after getting it back from mechanic) was likely caused by something the mechanic did wrong or failed to adjust properly when reassembling the door after installing the rubber seal. I realize my jiggering probably made matters worse and destroyed the regulator. But I can't help thinking it's some error on the mechanics part that left me out in the rain with a window stuck almost completely open.

Can anyone tell me whether mistake in reassembling the door could cause my initial window problem? Or is it, like the shop says, a complete coincidence that my window fails the first time I open it after they do extensive work in the door? Thanks!