Audi A3 2010

Audi a3 2010 I’ve had it for 4 years. the thread is worn and won’t hold the bolt in which is pushing up the injectors it won’t start but when I get it started it won’t hold for longer than 20 minutes driving it everything else is perfect I’ve got loads done to it new engine put in 12 months ago, new timing belt, brand new brake pads and right indicator light still in box. New alternator and new battery fitted under 6 months ago I also put it through the nct just before Christmas everything was perfect except the right indicator light and just never got around to rebooking hasn’t been heavily driven either