Exhaust header gasket replacement is part of regular maintenance. Depending on what make and model of sled, it's possible that the gaskets get changed out every other year, or sooner (Older Cats). And yup, black slime blows out of this area. (Usually below or beside where the header is bolted onto the cylinder).
You'll have to take the springs off, and remove the expansion chamber, remove the header, clean the mating surfaces on the cylinder and header, replace the gasket (#11 on the diagram), install and torque fasteners & re-install the expansion chamber. Be careful not to damage the exhaust socket seal between the header & expansion chamber (#13 on the diagram).
You may want to let whoever does your annual maintenance to do it, depending on your mechanical ability.