Not sure here but does it use plain motor oil and if so that could be for some type of oil system external tank or filter or pump,is that hole where u put the oil in and if so surely it takes a plug or a cap maybe its just missin ,i would try that manufactures web site there seems to always be some info on the web,or u could always go where the knowledge is ( the local race track) and local hot rod gatherings. local being loose terminology