Chris,
This engine has probably lost its outer bearing shield which prevents such leakage. Saito is a little more involved to change bearings due to valve timing. If the engine runs well then it is well worth replacing bearings and do both at the same time.
I guss I should have expalined, the shield is part of the bearing and covers the balls from dirt and most leakage. You will not be able to see the bearings if it is in place. It will be easy to spot when the rear prop hub is removed. Be aware, most inner bearings have the shield removed for lubrication and often the front one has the inner shield removed for the same reason.
Most commercial bearing supply houses have bearings in stock for substantially less than mfg. prices. Find someone to help you or obtaine a how-to book.