油 ........Well,he is a perv,a super perv,a perv with lots of time,and well,yu know.The oil might assist him in his activities,lol,j/k.Honestly,I have no clue why he has oil on his forehead protector.Its never been stated in the anime,nor the manga.I'm clueless to why he has it.

THe three sins of a ninja...spoiler tags becuase it hasn't been brought up yet in the anime.Though this won't spoil the story in anyway,it is tagged becuase it hasn't been mentioned in the anime

<span style='color:#D6DBE0'>3 sins of a ninah.
Booze
gambling
woman
</span>

Read at your own discretion.