smartguys, here's my advice on you O2 sensor issue:
Don't replace one or two. All four should be replaced by the time a boxster has 60k on the odometer. Replacing a couple of them only confuses the DME, with two having great sensitivity and the other two being dull in sensory capacity due to carbon build up.
When one goes, it throws off the DME and can cause the readers to show a bad MAF when it's not a bad MAF at all. This happened to me a while back.
www.oxygensensors.com has Bosch units for sale for something like $109 each and the connectors are correct. You'll need a O2 sensor tool that you can buy at Sears for $10 bucks.
Replacing all four at 60k has many benefits...
1) your MPG will go up, sometimes dramatically.
2) performance will go up too.
3) your wallet is much lighter, preventing back problems you're experiencing with so much extra cash in it.
I could feel a noticeable difference in low rpm torque after I did it and the engine idle was far more stable.
Best $450 I ever spent on the car. It's more fun to drive and it's paying me back each time I fill up with better fuel economy.