I recently bought a used SPT catback (sedan) from eBay. I've spent most of the day cleaning the thing up because the exhaust tips were black. I've purchased new gaskets (which only come as part of an $80 hardware kit from Subaru), nuts and bolts and some new hangers. In a previous life I used to be a tire and exhaust fitter... but I've forgotten most of it now. My question is, do I need to add any of that exhaust paste/sealant stuff around the gaskets? Or is adding a gasket and just bolting the pieces together sufficient?