Back in about '89-'90 I was the assistant manager at a fast oil change place, and we had a regular customer with a maroon '76 Aspen with a bullet-proof slant-six who got his oil changed with us regularly. I could hear him coming. I'd know it was him without even looking because of the distinctive TAP-TAP-TAP -TAP-TAP-TAP-TAP. We'd pull him in and he'd tell us to just change the oil and filter and don't bother checking all that other stuff, so that's what we'd do. We'd pull the plug and if more than a half a quart drained out we'd be surprised. After a filter swap, we'd fill it back up and restart it and it would go TAP-TAP-TAP-TAP-tap-tap-tap-ta-ta-ta-t-t-t-t-t-t-t- etc and he'd smile and pay and be on his way. Of course, we'd see him again in about 3 or 4 months, same thing, rinse and repeat. The tapping was his signal to get it changed. Fast forward to '97, after working as a manager at other locations I came back to that same station as the manager there and I'll be damned if that same guy in that same '76 Aspen didn't pull in for the same service with that same oil-leaking loud-ass tapping slant-six, still hanging in there...