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So my question is, could it be that the rad had sat at one time and corroded, then when it went back into use the owner fixed it with bars leak , and when they pressured it up with air it pushed it out,
or did they drop it and would this cause the problem.



It could have been patched with stop leak or it may just be old and thin. Either way it's not the shops fault for it leaking after a cleaning. If they dropped it you would see the dent(s). Just recore core it and