Part ID

I found this (well the dirty part of this) in the oil after an oil change and found the 2 clean bits in the rocker cover when checking the valve clearances.

One of the valves clearances was out by a whole lot too.

I'm assuming that it's something to do with the valve train a spacer or something but not having pulled one apart yet I'm not 100% sure which part it is though and how easy it's going to be to fix.

Any help appreciated, thanks.

looks like a hard o ring that some people fit under the rocker arms

is it metal or rubber ???

been mentioned here before about seals on the valve stems from the factory

It seems to be a plastic, just searched for the valve stem seals, seems like that'd be it. Thanks.

That's a bit less of a worry, I had all sorts of expensive thoughts, now I just have to figure out why it's running worse after the valve adjustment.