i was told, gm, upgraded mid-year 2020 production lm2 timing chains,...! My question is ,..how do i know what serial # engines started getting new updated chains,???. the new better chains have oil holes in the links,..!! without taking engine apart, who to know,..?..MY truck is in the "bad" valve cover group,.i,m waiting for leaking timing cover repair, parts on order,..was told 3 day job,...Asked if they can do valve cover at the same time,they said no,..:(..so,..am i driving an un-pinned grenade,...???