Hi all, freelander clutch help needed

hi all,
I've been searching this site for a while and am finally making my first post. Any help would be much appreciated.
I have an old V reg 1.8 freelander I bought to have some fun over the fields with the kids. It's got the typically common problem of extremely stiff gear selection but only when it gets hot.
I've put a new clutch in it, new master and slave, took prop off to see if any difference, new gearbox oil (mtf 94) and new ird oil 75/90 but still no better.
The slave bracket looks ok, but replaced anyway. It flex's a tiny bit so I've tried a 5mm packer in the release arm, no improvement. The release arm was free and easy to move when I took the box off.
Basically, the clutch pedal feels nice and it pulls away great, it's just getting the thing into gear once it's warmed up is impossible. I honestly don't know what else to try. Any suggestions would be most appreciated.

Any suggestions where I look next?

Worn synchros, wrong oil, mtf 94 is spec, clutch plate tight on splines

Thanks for the reply. Definitely has the correct oil in it. It's fine when cold, problems only come when it gets hot. Also fine when engine not running. Does this point to syncrows?

So it's new gearbox time?

Anyone? There's many threads with similar problems but very rarely does the op come back with what it actually was wrong!
Pretty sure synchros are fine as it's not grinding and goes in gear fine when cold.