Hmm how about the marks on JMan's face and what not? Are those made from oil to? Perhaps he even needs that to enter SM lol.
The marks appear because jiraiya is a true sage lol, naruto gets them too. Also, the oil evaporates too fast outside myobokusan hence why it would be impossible to use it outside.
So he needed those stuff to summon Ma/Pa but Ma can summon all those dudes that easy(Pa+Naruto+3 huge frogs)? Man those old toads are impresive.
Not that, what RK stated.