A failing alternator or failed one won't prevent an engine from running so long as the battery has enough juice. If anything, sometimes the car will be down on power because the coil isn't getting enough juice, but an alternator's main purpose in life is to charge the battery. It's only marginally involved in the continued operation of the engine once it's running.
The car just cutting out sometimes when driving down the road would never be an alternator problem unless the car dies and when you try to restart it, you don't even get so much as a click. If you've never had the engine fail to crank (it can crank without starting), your alternator's fine and so's your battery.
Oiled plug wires could explain it.
so he started messing around with it and pulled out the first spark plug and it was covered in oil.
I assume you mean the outside of the plug. If so, yes, it's a valve cover gasket and it's entirely possible for the car to be fussy about when it will and won't run on all cylinders.
The Taurus SHO (Yamaha V6 version) has its spark plugs situated between the camshafts and I'd assume this is a pretty typical layout anymore.
I was having an intermittent misfire problem with mine and the valve cover gasket turned out to be the exact culprit. The plugs in the rear cylinder bank were each immersed about 2 inches deep in oil, which had cracked the plug wire ends and softened the insulation on the plug wires. So sometimes the plugs would spark and sometimes they wouldn't.
Valve cover gasket, plug wires, and plugs had it running like a top.
Did you ever mention here what model of car you're dealing with and which engine?
With some cars in my past (and present, but not new) changing the valve cover gasket is a simple matter of four bolts and the PCV hose. Other cars (most of the ones I've got now) it's difficult to even SEE the valve covers, let alone remove them.
If it's as the guy at Advance thinks (and I concur), you're in for new plug wires (not a cheap date) and you might as well replace the spark plugs while you're at it (cheap insurance).
The thing to keep in mind on plug wires that I still do even on engines whose firing order I know like the back of my hand (1-8-4-3-6-5-7-2: Chevy smallblock, conjured from memory) is that you don't yank all the plug wires then replace them. You're almost guaranteed to get them wrong that way.
Remove one wire from the distributor and its spark plug, replace that spark plug, find the wire from the new set closest to that one in length, use it as the replacement, then move on to the next one.
