There's a fine balance between having a well sealed joint and one that's a complete and utter basterd to separate when you need it to come apart!

If it's only a tiny leak it may well soot-up and seal itself over time? Slip-on joints always seem to take a little while to settle.

You could try traditional exhaust sealant (the ones that cure with heat), but they aren't that flexible and can crack. They're also not easy to work with if it's a very fine gap you're trying to seal and they can be hard to remove too. HT silicone sealants are better for fine gaps, but only really on the cooler parts of the exhaust; if its the joint is where the link pipe meets the collector then it may well be too hot for it?

TBH, I've found kitchen foil is as good as anything for sealing slip-on joints. Just wrap round the male part, in as many layers as you need, force the female part on and peel off any excess that spills out. Makes a good seal and easy to separate too.

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