Well, to bring this issue to a close, I ended up getting a 2s 5Ah pack from HC recently. Took it apart and used one of the cells to replace the bad cell in the 5s pack. Took a while to balance it out since the storage charge I use was different than the charge level of the new cell. Ran it through a cycle in my MBX5 (my gentlest 5s setup), and pleased to say the pack ran fine. The original pack only had a cycle or two through it, so adding in a brand new cell should pose no usage mismatch problems.
I also picked up a lipo
voltmeter and it's actually pretty accurate. According to my Fluke meter, the reading on the device is about 0.02v off, but this error is consistent across all cells. So, either my meter needs a calibration tweak, or the lipo meter is a bit off. Either way, I can at least see the relative voltage levels across all cells with some accuracy. I have two other similar devices (
this and the meter-only version of
this). The former is VERY inaccurate, the latter is tolerable, but still quite a bit off.