Grammar, Usage / Oil has decayed in tank. [4]

Hi Everyone,

I am learning English language from last few months. but still sometime face some difficulty while making sentences like the one i mentioned below:

"The machine is not running from last few months so it might be possible that oil in tank would have been decayed. we need to empty the task as soon as possible"

this is the right sentence I have made. And if not what can be the right one. please suggest.