I can’t explain why you are getting different results with Gargravres and FasTrack, but since you are getting different results, that is something to look into. How good is your jumper? Did you verify continuity between the outer rails with a VOM?
Where are the sparks coming from? The pickups? The wheels? Does it spark constantly or only at track joints?
I wouldn’t use sandpaper on the pickup rollers. Use the alcohol or better yet mineral spirits if you have some. While you are oiling the pickup roller axle, also oil the pickup hinge.