[boosted k20]

why r u downshifting into first? I only shift down to 1st when im at a complete stop or if im going less than 10 mph.

If ur going like around 20 mph or faster and ur in 2nd gear, it will be pretty hard (but do-able) to shift down to 1st gear. maybe your forcing it into 1st and thats causing the grinding. I dont know man. sorry i aint too much help.
but i think that swapping out the whole tranny is cheaper instead of ripping apart the old tranny and replacing the synchros