i'm looking at buying this 91 explorer 4x4. its a 4.0 v6 and it makes a tapping noise that sounds like it doesn't have enough oil. the place i'm buyin it from is a shop/buy here pay here lot. the sales guy and his head mechanic said all older explorers that have sat for a while make this noise cause one of the lifters will freeze up, and they claim the noise will go away with daily driving and a good oil change with an additive to break it loose and it will run fine without freezing up again. has anyone run into this issue before with an explorer?