One thing that I know is that you have to check fuel trims with decent diagnostic software and what more important know how to read the graph. What’s also important is that sometimes oxygen sensors are getting sorry for improper term “lazy and are not reading/sending signal as they supposed to so even if they seem to be ok they actually aren’t and with almost 20yo sensors I wouldn’t be surprised that they are on the way out. However I am not mechanic and I am against throwing parts at the car especially fuel system related. I’d get it diagnosed since lean condition means more heat in the combustion chambers also check CCV/PCV operation since excessive pressure in crankcase is dangerous for those engines as well and what many doesn’t know, it leads to engine leaks.

 

My thoughts on O2 sensors on cars that are "of a certain age" (and / or mileage)...

1) After 100,000 or so miles their accuracy / performance can be suspect.
2) Gas is expensive, O2 sensors aren't (when you look at long-term costs, anyway). If there's even a tiny improvement in the efficiency of a car because of fresh O2 upstream sensors (aka "air / fuel sensors"), the price of the sensors will be quickly offset by improvements in gas mileage improvements. Worst thing that can happen is that you can just knock out a future maintenance issue by replacing them now.
3) Downstream O2 sensors serve no real purpose in life other than to make it difficult to get your car inspected (assuming you live in a state like Arizona where that's pretty much the entire "test" your car has to pass to earn its annual "drive it for another year merit badge"). Yes, they CAN clue you in to an actual bad catalytic converter, but generally they're just there to annoy you.