if the car is still under manufacturers warranty then if possible take it back to the dealership it was originally purchased from (if possible) and let them know of your concern. that way they can have it on record that you were proactive about the problem rather than just take it there if (hopefully not of course) it does decide to brake completely. prevention better than cure remember

from previous experience working at a dealership they didn't look to kindly on cars that came back with broken gearboxes as they immediately assume they have been abused etc and try to void warranty on it