Yes, it’s your exhaust temperature sensor, I used some black sealant around mine when it was installed, and also a couple of cable ties to secure it in place such that it doesn’t leak.
Take care with this item because if it leaks sea water resulting in the salt crystals around the probe, it might also be leaking exhaust fumes as well, albeit at a fairly slow rate. But if it does leak fumes, the fumes will contain carbon monoxide, and that can kill you.
