Whow! 300k? A jazz costs how much???
If manual ang jazz...mga 400k lng dapat sya...Hmm...Grabe pricing.
But then 6 months lng yun car, u might get them to replace the tranny for free.

Btw, I don't think its the belt, else your car won't move. Because of slippage or break. Might be the tranny is stuck in a position where there's weaker torque. ie. 4th (manual mode) <- gets ba?