I have a gravely zt1640 with a briggs and Stratton intek motor. It runs great and does not smoke. Occasionally it will stall like it is starving for fuel. After a restart it again runs fine. I notice that the fuel pump is dripping oil, is this a serious problem and is this the cause of the engine stalling. Already replaced oil, plug, fuel and oil filter, fuel pump and cleaned the carb and tanks. Any suggestions?