Fandini: I don't know enough myself to say if cleaning is the solution. In my case, I presumed, without really knowing, that mine simply had failed electronically, though it's plausible I suppose that the reactive surface was contaminated, I really can't say. Perhaps someone else reading this thread can answer your question. As I recall the diagnosis in my case was made by a good friend with an assortment of engine analyzers (he collects, repairs, and resells them), and he used a deductive process to isolate some electronic problem which I don't remember which pointed toward the O2 sensor. So I just replaced it. It was about $40, and I'd already wasted that much in fuel costs in the time since I realized I had a problem.
Regarding cleaning and reusing the sensor vs replacement....When I've got a part in hand, meaning removed from the vehicle, if it's something which could likely fail at some point and if its expected lifespan is approaching, I just replace with new as a preventative. Belts and hoses are good examples. Sensors likewise. If I had a manual transmission removed, I'd replace the clutch even if it had been working fine, just because I'm there, rather than push it another 10k and then have to pull the transmission again.
I certainly can't promise that the O2 sensor is your problem. You seem to have an assortment of issues, so you may have layers of problems working in combination, rather than just one problem. I suggest you find someone who can accurately diagnose your engine, even if you have to pay for it. Then you can set about repairing or replacing what is needed. With such low mileage, unless some serious problem such as overheating or oil sludging has occurred, this car ought to be well worth whatever repair is necessary. The 3.3L engine is an excellent one. The one in my 1990 has just shy of 300,000 miles, and still runs smooth though power is finally beginning to fall off. My 1996 runs well too, and with half the mileage, it is powerful and squeaky clean on California emissions tests.
I'd be curious to know what you finally find out, so please report back when you solve this one.