There is a small drilled hole (maybe 1/8" dia) on the port side of the gear housing at about the 10 o'clock position near the front. It appears to be design intent as if it were a weep hole yet, I can find no reference to it in the Merc service manual. The alternative is that the hole is the result of a prior repair procedure, or the motor struck something and I never noticed it before, or has the casting worn through which seems unlikely.
Does anyone know?