Hugo, now that the camshaft is out, pull out the HLAs and check that all the valves are at the same height, place a ruler across the tops of the valves, if one is down.....we know enough.
With a plastic hammer or something similar, give each valve top a strike (not too hard just enogh for the valve to move about 0.5cm and see if it returns.
fill each valve chamber with an egg cup of petrol and see if it stays in the chamber, and for how long.
check the teeth on both camshafts, for damage or broken teeth.
check the friction gear on the camshaft.
also check the camshaft seats (oil bearings) , for signs of grinding.
the only way this damage can be caused appart form fatigue is if the camshaft blocked.....the crankshaft will try and turn the camshaft and thus breaking the gear and shaft.
I will keep thinking of more things
