Having the cylinder 3 misfire but trying to find out which is the 3rd cylinder?

On a 4 cylinder it would be the third one back from the front of the engine. Check the coil.

The coil may be the issue, however my opinion is that the spark plug may be worn out , or additionally the spark plug wires are failing, arcing to ground. What complicates the matter on older vehicles with an oil leak is that the oil will well up in the spark plug hole. You will want to allow the engine to cool fully before attempting the spark plug change, gap .040 ish . I also suggest a little fuel injector cleaner now and again.