250 es rocker shaft oil leak

[Hair Bear Bunch]

Hi guys, I'm in trouble again!
'85 250 ES. On the left of the head, there are two 'screw heads' (page 107, fig 31 in Clymer manual), the front one is leaking oil. I'm assuming these aren't screwed in. I guess there is an 'O' ring on the end of the shaft. Is there any way of changing the 'O' ring or sealing the leak without removing the head?
Any help would be appreciated. Thanks.

[Dirtcrasher]

You don't have to remove the head, but you do have to remove the valve cover and remove the shaft.

[Hair Bear Bunch]

Thanks for that, as it's only a trace at the moment I think I'll leave it until I'm ready to do the timing chain. Can't have it out of action too many times!
Rob.