Hi,
before replacing the complete heads you can open the head from the cover-side; then loosen the cam chain sprocket and the screw to fix the solid bush; then you can tire out the camshaft with the cam chain sprocket-bolt. Attention: you must have set the piston at Top Dead Center (TDC) and the valve clearance should be checked.
Now you can see if the cam is good or must be replaced. A repair is not possible, yamaha offers original new cams (and by the way new valve rocker arms).
I hope I could help you. (Sorry for my bad english!)
Greetings Hartmut

You´re right! Thanks!
Hartmut