We have recently bought 2 model 2RS-4 vacuum pumps, the same after working 20 minutes or less they overheat and turn off, we understand this as protection, the question is normal that they cannot reach even 30 minutes.What could be happening with these pumps, can they tell us if this is normal or not?Our technician check the pump and reported that the screw (check picture) was almost falling and oil was licking from both pumps. Is that normal?