We had a very similar situation happen our our '11 Montana, while we were at our dealership having other work done I asked the tech how a guy could get into that narrow space without tearing everything apart. He told me to go to Home Depot and buy a tool similar to what was posted on the first page. The one from HD was not quite the same angle and it was Milwaukee brand, also he said to pick up a couple of hex extensions to fit on the end, use a drill and with one arm reach into the cavity and run a slightly larger screws into the track.
So once we got back home I did the purchase at HD, took all of the remaining screws out of the track, brought it down and applied a little construction adhesive on the track and installed slightly larger screws back in. That was the last time we had a problem with that pocket door coming off the track or "drooping" on us.
Good luck, it's going to be tight, mine was but I was able to get in there. :B
Dan