Make sure the pinion gear is clean but still lubricated, a good white silicon grease, enough to do the job but not so much that everything is covered in it and gets bunged up with crap!
On what side of the rail is the rail is the charge strip?
As a a temp measure you could stretch the spring in the charge pin to improve its push against the charge strip
Pull the brass pin from its housing and there is a spring behind it, these go soft with age so stretching it may help?
Depending on the hand of the lift the charge pins are different! Make sure you get the correct one!
The other thing to try is to move the stopping ramp up the rail a bit, the rail sometime compresses and shrinks where the rollers rub with the getting on and off which can cause the carriage to rock and loose its contact
It should be held in place by two screws? Just move it up one hole and see how it goes before you drill the other one
