When we were building engines we had a policy about standing behind the product , it had nothing to do with time , , often an engine would sit for a year or more before it was installed in a car , if we were responsible we fixed it if not well ... we would make it right but not at our cost .
One person we built an engine for had a lobe go flat on the cam , did he call us ... nope , I would have caught it on the valve lash reset , no instead he tried to blow the engine up & blame us for it LOL .
I would contact the seller , he may be happy to make it right for you .