Seal replacement can be hit or miss but failures are usually due to low quality part or user error. If you think about it, the new cooler comes with a new seal, which... you have to reinstall, same as just replacing the gasket... Curious, what brand of gasket did your friend use or did he use sealant maker?
Make sure you clean/prep the area well and the gasket is installed in the right orientation (there is a wrong way). Also, the through bolt is large 17mm (IIRC) head but you don't need to overtighten it; just need to sandwich the gasket.