[Blue Bowtie]

I'll third that opinion. Cleaning is just as important as lubricating. Further, WD40 is not a lubricant, but is a water-displacing rust preventive. When it was first formulated, it was never intended to be a lubricant, but like the common screwdriver, has been abused into the role of a "do everything" liquid. Tracks get Lubriplate or a similar lithium grease, hinges and latches get 20W oil, lock cylinders get dry graphite. It's right there in the manual.

Once you get it cleaned and lightly lubricated, it will be easier to see any distortion or alignment problems with any of the three roller sets - Don't forget the upper, even thought the outer and lower tracks seem to gather the most debris.