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.