It's a long shot... but perhaps try a bottle of
Lucas Fuel Treatment?
I generally
do not believe that these "octane boosters" and "fuel treatment" things really do much of anything. But . . .
1) My wife's DD is a 2010 Subaru Outback with about 60K miles. Last Fall, we noticed that the fuel gauge began stopping just below the "F" mark on fill-ups. Sound familiar? The gauge seemed accurate otherwise, so we decided that we'd look into getting it fixed (out of warranty) if it got any worse and would otherwise just sort of ignore it. It irritated me, but it was her DD and she didn't care as much. A month or so later, I was at a local AutoZone (like a PepBoys, etc) and they had this Lucas Fuel Treatment on sale at the checkout counter for like $3. Never used it before but thought, what the hell, right? Couldn't hurt anything. Added it and filled up the Outback. No change. Gauge still below F. Also no change in MPG, idle quality, or any of the other things it says it does, of course. But at the next fill-up, I'll be damned if that fuel gauge didn't go all the way to (and slightly past) the "F" like it used to. It's kept working normally ever since, going on 6+ months now. I'd sort of forgotten about it. This was before I bought my Z, so I didn't know anything about similar problems with Z's. Did the Lucas stuff fix it? I have no idea, but it sure seems like it might have. It was certainly worth $3, anyway.
2)So when I remembered this yesterday, I went out and bought another bottle for the Z (not on sale, $5) last night. Pulled into my garage with an already topped-up gas tank and the last LED
not lit. Added the stuff, drove around a few miles. No change, not lit. This morning, to my surprise,
all of the LED's are lit, as they should be. Perhaps fixed? Perhaps just coincidence? I know others have experienced intermittent behavior, so I can only assume that it won't stay fixed. But perhaps this stuff does have some sort of lubricating property that "helps" sticky sender units. No idea, I'm not a mechanic or chemical engineer. Time will tell...
Perhaps worth $5 for someone else to try and see if it makes a difference on your Z. Especially for those out of warranty. It couldn't hurt, anyway.