Alternator oil leak?

Hi anybody
I have a 1991 GPZ500S with an oil leak from the alternator cover, have removed the cover and the joint faces were a bit rough, have flatted them down and reassembled with silicon jointing although the Haynes manual makes no mention of any gasket. Looking at it I am not sure if there should be any oil in there, could this be due to a leaking crankshaft seal. Any suggestions would be appreciated Many thanks.