On the 4WD indicator light, I've had the rear passenger tire light go out. Occasionally it will light up (with the others) when I first start the vehicle, but quickly goes out. The other lights work properly and change correctly when I change from 2WD <-> Auto <-> 4Hi <-> 4Lo.

I'm 99% sure it just needs re-soldering / re-seating, but would just check to make sure it's not actually indicating a mechanical problem. As far as I can tell from the manual, the 4WD lights only change on a per-axle basis and aren't specific to individual tires.

I'm not familiar with this indicator light. Does it have four LEDs (2002+ instrument clusters have LEDs for the vast majority of the dummy lights), one for each tire?

LEDs should last practically the lifetime of the vehicle, barring a defective LED or a bad solder joint as you suggest. It's certainly possible to remove the instrument cluster, disassemble it, and reflow the solder, but it's not worth it just for that one tire indicator in my opinion. If it's working as designed, I'd leave it be.

That's the one; one light for each wheel. At times I swear that one LED is half-lit, just very dimly. The only other time I saw LEDs do that is when a strand of my Christmas lights failed... they were just barely visible in the darkness when the other strands were lit up bright.

One of the two backlights for my climate control has had the same issue since I bought this two years ago. It's out most of the time, but it'll come on for a few minutes maybe once a week. It's a bit annoying, but I haven't been motivated enough yet to disassemble the dash and fix it.

The only difference is that the climate control is off to the side and isn't an issue unless it's nighttime. The 4WD indicator is right in front of me and always on (or, rather, off).

I'd lean towards bad solder joints for both problems. Too bad neither PCBs are as accessible or a simple fix as the clock.

Just curious if you ever found a solution to your issue. I am having the same issue with my 2003 Pathfinder.

I just learned to live with it. So far all the other lights have continued to work, just that single tire light is out and so is the backlight for half my climate controls. If there's ever a need for me to get in behind the dash, then I'll definitely take care of it at that point.

Here's a nice how-to for removing the instrument cluster, back when members were all replacing the stock backlights with blue LEDs. Should be a good starting point on how to get in to there.