Transalp 600 - Shifting problem (see description UPDATE)

UPDATE: The problem wasn't the spring, the link mechanism was cracked open under the movement limiter pin. Pause at minute 3:40 and you will spot it. I missed that and later it broke apart.
While riding the Transalp wouldn't shift up from 2nd, sometime 3rd gear. Shifting down was ok. The suspect was the return spring from the shift drum mechanism. I got confirmation after opening the clutch cover to access that mechanism, the spring seemed to have got a little tired. I added a little of preload to the spring by deforming it a bit solved the case.