Almost from new I have had problems with the sram apex front mech throwing the chainoff the rings. More often refusing to move from the granny ring to the big ring. Not inexperienced I've returned it on a regular basis. Just had the bike serviced by Evans and after 30 miles back to square one. Throwing the chain and refusing to change up. Isthere a quick fix or do I scrap it and get a Shimano mech?