Gears intermittently sieze up after steep hills in low gears

Wanderer2010

I have a 2010 VW Golf 1.4 petrol and i noticed recently that when i go up very steep hills in first and second, a few minutes later the gears get gradually more difficult to set until its impossible to get into first gear, its as if the gearstick gets so stiff it cant be moved. The only way to rectify it is turning off the engine, pumping the clutch pedal a good few times and a hissing sound emits from it, the clutch is loose when i start to pump then gets resistant. I do this 2 or 3 times.

When i turn back the engine, the gears are smooth and glide from first onwards as normal but another steep hill and the problem returns. Noticed it a lot last week driving around hilly Kerry! There is obviously something going on, i put oil in it recently and it has enough coolant. Any ideas what could be behind this??

First and last gearbox oil installation/change was 2010... Ok, it was bit harsh rating. It is wild guess but is it possible the shifter linkages need adjustment and the motor and gearbox mounting pads are nearly gone. Not sure what I was smoking to get that idea....