white/blue is oil 
maybe this is the true reason why your selling it 
Like I said before, I'm not a mechanic, I'm only going on what I've been told, I was told it was running rich and to clean out the air filter system. If its oil, air or whatever, I have no interest in fixing it because I have a new car and just want rid of it.
Suggesting that I'm trying to flog it deceitfully knowing it has a different problem is not particularly constructive.
I posted on here looking for advice and if you don't have anything constructive to say then please don't waste your time or mine posting.