The sparkplug well gaskets always fall to bits and you need to prise the actual rocker off the right way or it'll break too - it's never a 20 min job for someone that hasn't done one before, double it at least for someone not that mechanically minded and taking their time.
Winding the rears in a click doesn't always work on old shoes or if the mechanism has buggeredd itself, like they seem to enjoy doing
No sorry I was referring to "everything" being brittle. I wasn't sure what you were referring to hence everything should not be brittle apart from the rocker cover.