I recently purchased an old Mott flail mower, model M255 according to the tag. The guy I bought it from didn’t know much about it. I replaced the drive belt and greased it but noticed a small round opening on the drive shaft cover between the gear box and the belt pulley. It’s obviously a machined opening, I’m just not sure it’s a vent hole or an access opening that I need to fabricate a cover for the opening. It appears to have some grease inside it. Any suggestions appreciated. Thanks