914 Exhaust pipe removal / install

The "Sealant" is most likely the High Temp Anti-Seize Compound.
The Copper Anti-Seize (1800°F) is usable but the Nickle Based Anti-Seize (2400°F) is preferred.
The Aluminum/Silver(Low Temp) colored type is not recommended.

It is on there to make it easier/possible to remove the fittings after being roasted by the exhaust.
If you need to pull the exhaust every time you remove the cowling,  you will definitely want to freshen the Anti-Seize every time.
It is not expensive considering that one bottle will last most of a lifetime.  My first bottle lasted ~30 years.
It is messy and does not like to clean up easily.

Use some solvent and paper towels to clean up the previous Anti-Seize to prevent forming a larger mess each time.