My gearbox has gone stiff too and theres a banging noise on biting point. I've thought about greasing the shaft and ball joint but I don't want to screw it up. I think the banging noise is probably the exhaust but the heatshield seems ok. I wouldn't be so sure that the PS pump needs replacing without changing the fluid first.

Stiff gear change when warm is, caused by the plastic bushes swelling on the gear linkage arm, on the front of the gearbox.
I had the same problem. Its an easy fix but a pain in the arse if you dont have a ramp.
You need to remove the plastic cover, if I remeber correctly there's about 6 bolts to remove this.
Then, take off the gear cables & the circlip on the pivot shaft. Once removed you may find melted or worn plastic stuck to the pivot shaft. Clean this up, then put back together with plenty of copper grease.
Thats all I did to mine & it seems to have worked.
Hope this helps.