High mileage 3400 maintainance

[Shiwnath]

So my 3400 has 231xxx Km(143xxx miles) on it and now that I have a full time job, I think it's time to look at the maintainance and preventative maintainance aspect of the engine instead of performance.

I believe The pre cat O2 sensor is still the original sensor that came with the car so I'm thinking of replacing because I remember when I was getting my car tuned a while back, the O2 live data graph had some flat spots and wasn't switching voltages like a fully operational o2 should be. To this day I still don't have any codes relating to a faulty o2 sensor, but i think it'll still help with my performance and gas mileage.

I know it's been a while since my PCV valve has been changed so that's something else to probably do as well. I pulled it out and shook it a bit and it wasn't freely opening and closing. It seemed a little sticky. Typically how often would these things need to be changed?

So far I've recently done AC Delco iridium plugs, NGK wires, magnaflow oem replacement cat, annual seafoaming. Other than what i've mentioned i'm not too sure where to go from here. These engines are stong and reliable and I want to see my Alero last me a long time before a engine rebuild is required so any input is welcomed.