HI Z world

I have a 1972 240Z with a standard 4 speed. While the car gets warmer the shifter gets harder to put into first. It gets to the point where I can not put her into first or second gear. Sometimes in reverse the the sifter pops out of gear. whe she is cool everthing seems ok,

New tranny?

Any Ideas from the Z Gurus of the world.

Thanks

Dragonz1972