I need some help, Y-blockers.  My stock 1954 256 merc has developed a leak at the crankcase oil breather assembly where the tube and adapter ass'y. join the filter can (cover).  I pulled the filter can from the top side, removed the old, hard, brittle cardboard gasket and replaced it with a proper sized o-ring.  I reassembled it, being sure the o-ring stayed in place, and now it leaks more than before.  I really expected that the o-ring would be better than the gasket.  Also, oil is pooling in the top of the breather tube ass'y. where the bolts retain it and the oil return tube to the block.  Shouldn't the oil return tube empty this portion of the breather assembly?  I'm going to disassemble it again, this time removing it all from the side of the block to be sure that the oil return tube is not plugged.  What am I missing here?  Also, should I add some sort of sealer to the o-ring and mating surfaces?