Harmonic balancer question

Something doesn't sound right but I'm having a hard time visualizing what's happening. The harmonic balancer is actually two pieces, a center hub bolted to the crankshaft, and an outer ring glued to the hub. On your engine the drive pulley is bolted on; it's not part of the outer ring. If just the pulley came loose, it would fall off but not cause an oil leak. Since you do have oil leaking, it suggests the center bolt has worked loose and the balancer has walked out and is not engaged with the crankshaft. That will expose a seal and let oil leak out rather quickly.

The fix might be as simple as pushing the balancer back on and tightening the bolt, but this happened to my minivan a few years ago and the hub got all chewed up. Cost me five bucks for a used one from the salvage yard. No damage occurred to the crankshaft snout. If you do try to push it back on, there is a keyway that has to slide through a groove in the center of the hub so you'll have to rotate it until they line up. There's also a chance the key fell out but they're usually in there pretty tight.

A lot of manufacturers are having trouble with their harmonic balancers. Auto parts stores have fat catalogs showing nothing but replacements. There are three different units for the Taurus. One is plastic and looks like there's no way it could possibly hold up to the stresses of running a belt, but that one doesn't go into the oil seal.