dont get me wrong, chop shop selling price and and independent selling price differs my fren. and especially in this case where a gearbox and its internals are considered wear and tear item.
no doubt, RM300 for your gearbox is quite low but on the reality that's what you should expect.
example, a shop may sell one 4G93 half cut for RM5K (example) but at ZTH marketplace you can get chaper than that. why? same thing laa...