I deal with this sort of thing every day at the dealership that I work at. Until your service guy can reproduce the problem , any repair will just be a guess. If your lucky enough to be near your local shop keep an eye on the vehicle as you drive it daily. If it starts to act up , whip into the shop , grab your service guy so he can see the problem in person. It's no alway's easy but it's the one way to be sure. Just my opinion.