oil leak?

[Herr Mustang]

I have a 1988 johnson 88 spl. it has oil leaking out from under the plastic cowl just above the two exhaust ports down the sides of the motor. very thick black oil. on examining it, it looks like the gasket from the bottom of the power head where it connects to the transmission. my question is, is that something that needs immediate fixing? it does not seem to effect its performance at all. also, at idle the motor coughs occasionally. doesn't seem to matter if its cold or hot, but sometimes is enough to stall the engine. thanks for any help.