With just 10 hours recording & playback I would say you should get the repair done under warenty! If not shout long & loud at them until they do the repair for free
MiniDV is not a robust format. The heads are very small and easily damaged or knocked out of alignment.
Have the dropouts occurred ever since the cam was returned from repair. If so then I would think that it is down to them. Even if not it could be caused by a lot of different things such as a dry solder joint etc which is a manufacturing fault.
Head cleaning tapes are the best way to clean DV heads and as long as you only use them once at a time, and only when needed should cause no damage.
Mark.