Sounds like a leak in your heater core. If it is a heater core leak, the oily residue is vaporized antifreeze that has returned to a liquid or sold state.

It doesn't take much coolant to cause the issue. You may not notice the leak as the carpet often hides the damp which is under the carpet and it is rubber backed. Often you find the damp in the rear RH foot well first before you notice it in the drivers side. It may not be a big leak, but may be sli...

If you go the eBay cheapo core route (as I have done before) make sure you run it through the dishwasher before installing. Otherwise you'll be smelling an oil residue from manufacturing for months.

Yes heater core and water drain lines are suspects but note carefully what Neil said: Leaky o-rings are a common cause of this, especially when it first shows up in the winter. Metal pipes shrink in the cold, and old o-rings leak. Pull the carpet up and look at where the heater pipes go into the fir...

The idiot light for the alternator is pretty simple
and doesn’t generally trip any codes in
the OBD2 computer.
May have been a bad battery, a poor cable connection
or possibly the first signs of a charging
system issue. Keep Driving!

On ECC...if there are no blinking ac/rec lights on every startup,there are no stored codes and if there was any ...they clear themselves automatically once the problem is solved. Thermistor itself(if you are talking about cabin temperature sensor on the dash)if it's bad it will not prevent blower fa...

The MAFS rarely fail, your numbers look ok.

When was the last refresh of plugs, cap, rotor, and plug wires? When these cars sits theseparts still corrode and degrade. Plugs are 15-30k replacement interval parts