Since the rollers in each of the mechanisms are not sealed bearings (they have dust shields but they are definitely not "sealed" bearings), they can gum up with a lot of dirt over the years. Lubing the track does nothing to help them. Getting lube inside the bearing can help but you really need to get the dirt out if you want to free up the wheels. Unfortunately, there really is no easy way to do this and in many cases the bearings are just too far gone. Sometimes you can flood the bearing with a solvent cleaner and blow out some of the gunk with compressed air (be careful not to let the bearing spin out of control when you blow air into it) then afterwards flood it with lube.
They're really freakin' cheap bearings... Like the lowest quality garbage bearing you could ever actually put in this vehicle and still get away with it (Thanks Ford...
). All of the slider door hinges I've worked on have been coated in dirt and debris so it's no wonder the bearings get all gunked up. Could easily be solved with sealed bearings but Ford is too cheap and the E-series gets little engineering love.
The bearings aren't "replaceable" on an individual basis. Each of them is riveted to their respective slider assemblies so to replace a bearing means to replace the whole hinge at the back or the slider at the bottom front or the slider at the top front.
If you're taking your door completely off to replace all of the parts, the best starting point is to line up the hinge assembly (or the bottom front or top front assemblies) using the paint as a guide. When you remove the bolts, there is a crisp outline of where the bolts used to line up in the paint. I can't remember off the top of my head but I don't think the bottom front assembly has much adjustment. The top front has very little adjustment and only in one direction. The rear hinge has the most adjustment and I've posted some tips for aligning the door after a hinge install on my website.
http://www.mgmetalworks.com/hinge.pdf. Towards the end of the tutorial I write about adjusting the hinge in the door and things to consider for proper fitment. You're welcome to contact me offline as well if you need more information.