Oil analysis

Definitely check the info/forums at bobistheoilguy.com .

My guess would piston skirt wear. Perhaps caused by ring or ring land problems? Maybe wet/dry compression testing is in order?

Maybe an injector is failing 'open'? Also, very short trips could mean the car is in 'choke' mode more. A failed Engine Temp Sensor (NOT the coolant gauge sender) can keep a car in 'choke' mode - as if it never warms up. Could lead to higher fuel use and perhaps contamination if coupled with short trips (reduced opportunity to drive out volatiles). I also wonder if a bad PCV Valve could somehow contribute to the problem?

I'm not oil expert, but will put in my two cents. That may be all this si worth though...

You say that the deltas are in the last two samples as compared to earlier ones. Were the last two samples of oil used in the winter, whereas earlier ones were only collected in warmer months, then no experience last winter? Like you perhaps just started this sampling a year or so ago? If so, it might be seasonal differences. Cold weather makes for harder starts, which causes more wear. Also, in cold weather, fuel doesn't atomize as well, letting some of it condense on the cold cylinder walls, then getting washed off into your oil while the piston is above that area.

Total theory. I'd suggest looking into the possibility that this is seasonal if you don't have previous winter experience to counter that.

Bill

Also, pulling the spark plugs, marking them with their cyl number, and comparing side-by-side might point to which cylinder is the culprit - if there IS only one.