This should help.
There are 2 ball bearing within the two dimples on each end. Total 8 ball bearing per seat runner.
The dimples in the track limit the ball bearing travel.
To remove the top slider, punch the pin out. The 4 ball bearings will then slide out of that end. Same procedure for the other end.
If you find the top slider does not slide easily, find out where the ball bearing resistance is, ball bearing stops moving, then address the outer or inner rail. I needed to squeeze the inner rail in, in that section, to provide more room for the ball bearing to move.
I've include a photo of the cut outs for the hand lever pin to lock in.
Everything need to be cleaned including the spring and lever for it to work effortlessly.
I found that greasing things does not work out. The grease hardens, collects dirt/debris and inhibits free movement after a while.
I cleaned everything, rails, springs, ball bearings. Assembled it grease/lubrication free. Now it slides smoothly without friction anywhere.
Best of luck.