Whelp, replaced the reed, put a pad back on, fixed a broken key, and took it for a test drive… sounds really good! Still pretty leaky, though. I replaced the main gaskets and it’s not much better, so I wonder if it’s the pads.
Unfortunately, the low G reed is also apparently bad — it’s sounding at a slightly flat F. This makes me thing the reed might be about to snap? Is that a fair guess? There is nothing obstructing the reed or whatever — it’s just very, very flat (and has no signs of having been tuned in any abnormal way, etc.)