Not sure if the gasket is similar to that of the newer bikes,is it a hollow copper O-ring that ends up crushing flat?,I would recommend keeping it,even reusing the old one if it is decent shape,if missing install one,since I believe it isolates the pipe from the cylinder.New o-rings might stop the spooge but a little silicone can't hurt,just spread a thin layer over the O-rings before you install the pipe and it should cure the leak,make sure to clean the area on the pipe and cylinder with some contact cleaner before applying the silicone for a good bond.