One string of three white LEDs in the left handlebar of Mary’s Handi-Quilter HQ Sixteen died over the past two decades:
A view minus the glare:
I replaced all 15 LEDs with new-old-stock white LEDs from my stash, while neglecting to pay close attention to the silkscreened orientation marks.
I used up a lot of solder wick while re-extracting seven of the LEDs :
The LED in the front-right corner is in the string with the two LEDs just above it, while pointing in the opposite direction. This definitely violates the Principle of Least Surprise.
Being of sound mind, I tested all the replacement LEDs before installing them:
Which tedious process weeded out a couple of deaders, one with its case on backwards, and a handful of completely different white LEDs evidently from a different manufacturing batch. Buying low-budget LEDs directly from a sketchy source halfway around the planet does have its downsides.
Being that type of guy, I also tested the removed LEDs. Weirdly, one of the strings had two dead LEDs, which suggests one failed short and the increased current took another LED down with it.
Two of the three strings in the central PCB had died and were replaced without incident: they all pointed in the same direction and I can deal with consistency.
The Smell of Molten Projects in the Morning 
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[…] the Handi-Quilter HQ Sixteen handlebars at a useful angle aimed the main PCB’s white LEDs at the front of the arm, rather than down at the […]
[…] Typical 12 V systems have parallel strings of three LEDs in series, so you (well, I) often see automobiles with three adjacent dead LEDs. That turned out to be true with the 15 V (-ish) LEDs in the HQ Sixteen machine I’ve been refurbishing. […]