I am approaching readiness on the Heater Core job.I have a heated garage where i can do it and have my laptop plugged in to at least reference offline the available DIY guides.In reading other posts about the job it seems some find the O-Rings were the culprit and the core still intact, other find the core leaking.I plan on buying the core but if I first try just replacing the O-Rings and that stops my leak would i be well advised to go ahead and replace the core while i have it accessible or save the money and return the core keeping the old one in place.In other words do the cores end up failing ultimately anyway?I wonder if having faulty Water/heater valves resulted in the failure of whatever is leaking down there.... I knew i should have replaced those when i learned they were bad months ago..