GMC Safari / Chevy Astro Van Sticking Sliding Door - Let's Figure This Out

Ever since I bought this van, I've had to open the sliding door with 2 hands. As you can image this is very annoying when you're carrying something.

The first thing I did was to inspect for broken parts or parts with excessive wear. Not finding anything obvious, I starting spraying everything with a lubricant.

Much to my surprise, this solved the problem.