u/2014WrxHatch0202

Bought my 2014 wrx used. Got 23k out of the built bottom end ej255 that was put in by previous owners, unsure of milage that was on the motor. Went in for a misfire on cylinder 1 and discovered a hairline crack in the cylinder. Shop says it wasn’t my fault at all and my pistons still look shiny. What in the heck could have caused this random failure? Maintained it religiously oil changes every 5k running 5w-40 motul. Had it professionally protuned a week before this happened. Never seen anywhere near redline, never did back to back pulls etc. could it be from the bad tune the previous owners were running or just a freak random failure? Had this car a total of 9 months and now have to do an engine rebuild.