FWIW last spring I put the exhaust on a 1958 Evinrude together with two thin gaskets and the baffle plate, no sealer. Result was black goop from the exhaust leaking into the bottom tray of the powerhead. See photo. Looks like the thin gaskets were leaking. I will replace the gaskets and this time use E/J/ BRP part number 508235 sealant. 
