[DanEC]

Thanks for the reply - I was waiting to see if anyone would comment about the sound at the side vent. I may need to looks for a header gasket alternative - those copper gaskets are far too expensive for a single use.

Taking the collector off at the header pipe slip joint involves loosening the header pipes slightly and then twisting and moving the whole thing back and forth to loosen the collector and get it to slide off. All that movement may do some damage to the gaskets during removal.