I doubt you would have gotten 3 bad pumps or had 3 go bad in a short time of little use .... the drainback you hear is oil from the filter and particularly from the top end, not gas, but yes it's running way rich - don't know if that would send a lot of gas into the crankcase, but definitely some would be washing down the cylinder walls ... not a good thing to be running it repeatedly at idle even if you think you're warming it up, you really need to drive it to clear the moisture from inside that's condensing on everything each time you shut it down .... the fact that it needs choke to run then dies says you have a carb/fuel problem, check for vacuum/intake leaks
Bill
