I have a sliding glass door, approx. 80″(high) x 45″(wide), fitted to slide along a metal track. About 6″ from the closing edge of the door, the door becomes almost impossible to close. I tried spraying WD-40 on the bottom of the track, which works for a few times, but then loses its lugubriousness(if that’s a word). What can I do to that track to make the door slide easily and smoothly?