Rocker shafts wear fairly quickly. The upside to this used to be that the rocker bushes lasted longer, but later sintered rockers run without bushes. It is easier and less expensive to replace the rocker shaft!
Fits all models but beware as some early cars pre 1967 had the locating post hole in the 1st post but this was replaced by moving it to the 2nd post to stop flex and wear and breakage. Make sure you still have the oil hole post feed in the right place when converting. This standard original type shaft has the 2,5mm wall thicknessis but see
C-AEG399 which has an upgraded 3.7mm wall thickness.
Posts with oil holes 12G1926
post with locking hole 12G1927