did mine this year on the way to the Leicester RSOC show, but at least its an easy fix, well was on mine, put another rocker arm and it was as good as new! The brake on the rocker arm was a clean cut so no bits got in the engine, seems to be common on high reving ERST.

As for price, I think buton sell them for £12 each, but u might as well replace all the shims and nuts at the same time, so I wreckon ur looking at £130ish!