Relay 2003 gets stuck in gear

[Oliver53]

2003 Relay 2.0 HDI. Just arrived at MOT after 5 miles drive and van gets stuck in 1st gear, can't move it out, not even neutral...MOT guys are busy and won't look at it. Calling wife to bring tools. Any ideas?

[Oliver53]

Drove it back home in first gear, on arrival the gear change suddenly becomes working again. Changed gear oil, when tried to drive it got stuck again now in reverse. Popped the three linkage ball joints off, gear stick moves freely but not the shaft/arms on the box. Surely it's the gearbox at fault. What options do I have now? Is taking the box off the van the only way forward?

[Oliver53]

Tried a trick someone told me that is to release clutch suddenly with acceleration pedal down to make a short jerk. That occasionally can free the gear change up - not 100% normal though: reverse, 1st, 3rd, 4th and 5th can be selected, but no 2nd, and not really a neutral either - the van would want to move in the supposedly neutral position when clutch is released. And it will get stuck again when try to drive.