[soundman98]

how are you using the clutch and gears?

so you come up to a stoplight. you were in 4th. of course clutch in, do you go to neutral? row back down through the gears? do you sit on the clutch for the duration of the stop light, or only clutch-in again when the light goes green?

while sitting at the light, have you tried clutching out for a second to spin up the transmission and re-try 1st?

i've found if i roll to a stop in another gear, and then sit on the clutch(if i'm expecting it to be a short light), i'll sometimes have a similar issue getting into 1st, but only sometimes. as you, i'll either find another gear that will go in(usually 2nd goes in fine at that point) to move the syncro's and it'll mesh with 1st then, or i'll also just drop back to neutral, clutch-out for a second to spin the input shaft slightly, and it'll usually mesh again as it ought to in 1st.