Xoutpost.com - 2001 X5 3.0 misfire codes

Hi there! First post here, hopefully I'll be able to stick around with more than just questions about problems...

I'm looking at buying an E53. There's one locally that's perfect for me---I like the color combo, it's a 5-speed (must have for me), and it's got the options I want. It also runs and drives great, for having 148K on it. Seriously, I never expected an SUV to be so fun to drive. The catch? The SES light is on, returning a group of codes, which I assume are all related. Now, being a DIYer, I figure this might be an opportunity to talk the dealer down on price and fix the problem myself. So, I'm hoping to compile a list of what all could possibly be wrong, and from there, figure out whether it's worth the trouble.

Here are the codes:

P0300 - Random / Multiple Cylinder Misfire
P0302 - Cylinder #2 Misfire
P0304 - Cylinder #4 Misfire
P0313 (x2) - Misfire Detected with Low Fuel
P0161 - O2 Sensor Heater Failure

Anyone had these codes? What was the cause? I want to stress that when I looked at it, it fired right up, and it idled and ran smooth as silk. If the light wasn't on, I never would have known it had a problem.

Here's what I've read are the most common potential issues:

- Bad post-cat O2 sensor(s)
- Fault in the O2 sensor heater circuit
- Clogged catalytic converter
- Fuel pump going out
- Clogged / dirty fuel filter
- Dirty fuel injectors

And less likely, since the car exhibits no real signs of trouble:

- Dirty / faulty MAF
- Large vacuum leak
- Faulty DISA system
- Faulty CVV / oil-air separator system

So basically it could be as simple as running some fuel injector cleaner through the system and as complex as a head gasket. I think a problem with one or more O2 sensors is almost guaranteed. But, could an O2 sensor cause ALL of those codes? It's just bizarre that the car seemingly runs fine.