Sweet! I was thinking it sounded like something with ignition, I'm glad you found it. I did something similar with an old S-10 Blazer I used to have. I started out replacing one plug wire at a time but somehow ended up with them all apart and no idea how they went back together. I finally figured it out after hunting through service manuals for an hour.

Is the leak from around the edge of the pan? Make sure all those bolts and nuts are there and tight. Might be worthwhile to change that gasket too. Seeya.

As for the check engine light, look down by your ECU and you'll see a little 2 plug green plug (it may be in a little rubber boot). Just take a little wire and jump those two connections. Turn the key on and the check engine light will flash. Could how many long flashes and short flashes you get. There are a lot of good of sites out there with better explanations and lists of what each code means (sorry, I'm not on my computer so I don't have any). Seeya.