I would say things could be far from fine, if there is shards of metal in your gearbox the damage will have been done already, the gearbox wont last long and a new second hand box will cost you a few hundred. I have to agree with above gearbox oil stinks like eggs farts its foul. Personally i would think your gearbox will be fine, sounds like they were trying to scare you into an oil change. Least your clutch is ok, you need to re mortgage to get that fixed.