You'll have to be more specific. You don't say what failed. Those B&G pumps do need oil, but you don't "fill" the reservoir. They take a few drops at the seal and a drop or two at each end of the motor. Oiling once a season is plenty and only a couple drops at most.
I've seen them run for many years with no attention or any oiling.
The most likely failure on these is the spring drive coupling, and according to B&G, the most likely reason for this to fail is over oiling. Too much oil softens the motor mounts which lets the motor sag and run out of allignment, which stresses the coupling. The coupling is a fairly easy part to replace, but it will fail again if the motor mounts are weak.
Too late now, but it's probably better to go with a system lubricated pump next time, like a Grundfoss or Taco.
Keeping a "paper trail", as suggested, is ridiculous. It's not about building a legal case of who is to blame years down the road in the event of a failure you think happened before it should have. Sheesh. It's about what is the correct oil and what is the correct technique.
Those pumps all used to come with a small amount of oil in a plastic packet that was to be kept with the pump for future use. A good alternative to non-detergent electric motor oil is Mobil 1. I'm sure your vacuum pump oil is fine. If anything, it probably has less volatles to evaporate. Probably better than standard motor oil and definitely better than transmission fluid.
