Is the oil overfull and smelling of gas in the oil? When did this start? When did mower last run?
What is the engine model number? 950 is a series. Twin engine or single cylinder? Looks to be single cylinder engine. The engine has a crankcase vent and hosethat goes into the air intake, before the carburetor, is this vent open?
1375 is the vent cover, goes on top of the crankcase. See parts link below.