Sticking Sliding Door
I found dry graphite to work wonders on such sticky situations, especially sliding doors. I have a super heavy vinyl door with no runners. Spraying WD40 or any other "wet" oils will also attract dirt and dust in no time....trust me from my experience.
I also tried the good old fashioned SC Johnsons wax paste. It comes in a large metal tin and works great on everything. I wiped it all over the bottom and top rails and after several minutes wipe it dry. It will leave a residue that is dry and lubricated. It works well and doesn't pick up dirt.
I also use this stuff on tools, saw blades, and anything that could be improved by reducing friction.