Any non-detergent 20wt motor will do from an auto parts store or 3-in-1 makes a 20 weight, sold a k-mart or hardware store, but will cost more that the a regular quart of motor oil.
There is a 3 in 1 oil that says 20wt on it, it is not the normal 3 in 1.
sae 5w 20 is not the one, at your auto parts store look for or ask for help to find non-detergent sae 20wt oil.
Reaper10
3 in 1 makes an oil specifically for electrical motors...do not know what the difference is...but after almost 300 bucks for the pumps..figured the 3 bucks or so wasnt too bad a price...