You may have a bent push rod (clutch)
Or the syncro hubs are wearing out, they normally crunch like fudge into second, and make 1st really tight, unless you slot it into second, then back into first, dunno why this works, but it does.
If the box is knackered, there are companies out there that will rebuild the box for less than £100, and you can get the bearing kits from e-bay for about £70. I know that it sounds expensive, but you get a fully rebuilt box for a bit more than a second hand box with an un-known history.
kraM