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I have a Mazworx header and they did not weld the inner part of the tubes going into the collector. Last night i put some solder on them just to see if the AFRs changed as the leak is pre-O2 sensor. The AFRs are reading quite a bit richer than they were before, so the leak is affecting the readings. What should i use to fill the gaps? I thought about some sort of putty or epoxy because there is no way to get a welder in there. Anyone had any experience? I did some random internet searching, and some suggested Pyro-Putty, JB Weld, or even high temp silicone.