Got oil gallery cleaned, but another problem found, 3 of the tappets had this centre "button" deattached and easly falling off when removing tappets from the engine, this metal O ring that should hold it is just inside the tappet

I was thinking can I fix theese on my own with new O rings? or should I get the new ones?
Bought from protechmotorsportltd on ebay lately, I dunno maybe they are just all crap