I would suggest you not try to save a buck or take the easy way out. Not all rubber like materials are compatible with engine oil. Say you go to the hardware store and all they have in stock are natural rubber or EPDM O-rings. Once those are exposed to engine oil they will swell then begin to disintegrate. Now you will have particulates circulating through your crank case. I'm sure you wouldn't want one of those particles working its way into a small orifice somewhere and causing no end of mischief. :0

Go with what you know.