I have a small exhaust leak in my winter beater ('87 Chevrolet Sprint) from
the top of the joint where the header meets the pipe. I have to stop the
leak (at least temporarily)before I can have the vehicle emissions tested
(required in some parts of Ontario). I wanted to replace the pipe but its
sold as one peice which includes the catalitic converter, meaning I'm
looking at $500 US / $750 CAD (More than the car is worth - and I only drive
it maybe 3000 miles / 5000 km a year). If I wanted to cut the pipe at the
cat and then weld a new one in, I'd need to weld alluminum to steel which I
can't do (I don't own a torch and it is a specialized job). So I'm looking
for caulking or something that will resist high temeratures (for 2 hours)
but also be somewhat flexible (the joint is secured by bolts on springs)
does such an animal exist?

As long as I can get the leak plugged for 2 hours I can get the thing on the
emissions machine. Even if I fail the test, the cap on the repair bill is
$130 US / $200 CAD (but the cap doesn't apply to pre-test repairs).

Thanks,
Chris