Thanks!
Capacitors are one of those major failure points in older electronics. Sometimes the failure is rather forgiving and the power supply simply won't start up, other times it can be rather awful and messy, like it was in this case.
I'm not exactly a professional myself, I studied Electronics in Grade 11 (2008) and Electrotechnology in Grade 12 (2009). I immediately went to Apple and became a Certified Technician, so component-level repairs were never something I did that frequently. I'm only 22 mind you, so hopefully there's plenty of time to learn a little more and continue working on these skills.
I bought a rather cheap
20/130W Turbo Soldering Iron for $18.00 as a temporary measure when my old iron burned out, expecting to only get around 6 months out of it, but so far it's continued working perfectly. I hear the Turbo button can damage the iron or wear it out prematurely when used frequently, so I've stayed away from it.
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Of course you can get much, much better irons if you're willing to spend a little more. I'd always recommend a proper temperature controlled iron if you're willing to do serious soldering. Not that it's impossible to use a cheap iron, but it does take a little more effort and it can be difficult to get a professional result sometimes.
MacTech68: I think you could be on to something there. I've always noticed the behaviour of the Shift Keys to be consistent with the behaviour outlined in that Apple support article. I'll have to disconnect the wires at some point and see if the behaviour changes to be sure, but it would make sense, especially since it sounds like it was fairly common for the era.