Need a sealant for my furnace exhaust

I have an oil burning furnace that has developed a small leak in the exhaust pipe that leads outdoors. The holes looked as if they had burned through due to the heat. Unfortunately when the furnace is on I sometimes smell a little exhaust in the basement close to the furnace as the exhaust is leaking out through one of two very small holes. During my annual maintenance similar holes (very small) were sealed by the repair man using a thick red sealant that he dabbed over the hole with his finger. Just wondering what type of sealant he used and where I might be able to find it?
Thanks for your help.
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It is probably high temp RTV. If your exhaust is rotting out, it should probably be replaced. Depending on the length, it shouldn't be more that $30 worth of 26 gauge pipe, unless you have B-vent or something else.
JK
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The hole was probably put there on purpose. About the size of a thick pencil? That is where they will do their efficiency test after cleaning. It probably should be filled in, but it's not going to hurt anything. Think about it:
Doesn't your smoke pipe have a draft regulator on it? (It's that "flapper" thing that squeaks and bangs when the wind blows). Look how big THAT hole is! If it IS in fact holes that have burned through, it sounds like all of your pipe needs to be replaced. If it's just a hole that needs to be patched, get some high temp RTV sealand or simple furnace cement and seal it. Otherwise, don't sweat it.
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