Questions muna:
1. Properly adjusted ba clutch mo - kung hydraulic, na-bleed na ba ng husto? kung cable, tama ba adjustment?
2. Sure ka ba na tama apak mo sa clutch?
3. Does it happen sa particular gear or pair of gear lang, say 1st/2nd gear or 3rd/4th gear lang sya sumasabit?

If your answer is YES - YES - YES...

...malamang worn out na yun synchronizer gear and synchronizer keys pare ko. That means your tranny needs to be opened for overhaul. Expect to spend anywhere from 3k to 10k, depende kung complete or partial overhaul gagawin mo.

aray ko po!