Well, I thought this discussion would have gotten a bit more traction, but since it didn't, this probably isn't a common issue.
That being said, after looking into this a bit, primarily looking at photos of similar watches on the interwebz, some showing what appears to be somewhat similar condition(s), as well as some info/photos of the actual internal arrangement/construction of these types of watches, I am of the opinion that it is fairly unlikely the 'residue' in question is anything particularly nefarious. As pointed out, the watch, and by logical conclusion, likely the battery, are working just fine. I didn't stumble upon particular common battery leakage problems. From what I can tell, the condition of my watch hasn't changed at all.
As such, unless I'm missing something (please let me know if I am), it's in all likelihood some type of benign sealant and I plan to carry on using it.
At some point down the road, I want to add something along the lines of of a Fenix 6X with the slightly bigger screen to give tired eyes a little more legibility.
Cheers,
- M