I couldn't figure out how to get the door off without major deconstruction. It looks like they slid the hatch into the top and bottom rails, then embedded the metal hatch frame into the boat. The only way to really get to the rollers, is to remove the interior wood trim, remove all the screws attaching the hatch frame, they cut out all the caulk they used on it, hoping to God that 5200 did not get applied. Even if I did want to go through all that, the door wouldn't slide far enough aft to get at all the screws.
I thought I might be able to get a wrench up on top roller bolts, but even if I could there isn't enough room to get the nut off then slide the bolt out to free the roller.
So, being a former US Marine, I applied brute force. I found that if I slammed the door open, it would jam and be difficult to close again. If I applied constant pressure, the door would slide incrementally and emit a fairly uncomfortable crunching sound with a gray-ish dust.
I went back to my “redneck” trouble shooting guide: “If it’s supposed to move and it don’t; WD-40.” I liberally applied WD-40, and like magic, each push of the door resulted in move crunching, more dust (now in WD-40), and more movement. I eventually got the door to slide all the way to the end of the track, with that little stop at the bottom removed. I could get my fingertip up into the track sufficiently to feel the rear roller, or lack thereof. It feels like the roller deteriorated sufficiently to start unravelling in layers.
I’ve got the sliding door working good enough to get by. One of my future projects will be getting the frame out of the helm opening and fixing it properly with good replacement rollers, good enough to last another 21 years. But that won’t be for a while.