Just to add a point about the guide. We've noticed that sometimes the car will bounce out of it's slot especially on a long straight.
As Spring moves on and the days are getting warmer. I find my track moving a bit on my table. The long straight is far from smooth and the bumps (Scalextric Sport) are like cavitation ridges in a dirt road causing the Challenger to deslot two thirds of the way down the straight and crash off into the sand trap at the end.
To prevent this, make the guide bigger by squeezing in a vice. Works fine now.
Here is the 'before' and 'after':