Regards the Singer Motor Lube going bad:
As I have said I have many tubes of the old stuff. Mostly partial tubes. I have used much of it on my 15-91 motor gears and found that once it was out of the tube the consistency was unchanged. The grease closest to the spout was somewhat dried out, but that inside was OK. Once mixed up I couldn't see any difference between the old stuff and the new stuff.
I'm not a chemist, nor an industry rep, but I have greases that I bought when I was a teenager for use in my bicycle bearings that is still good.
Other grease such as the white lithium grease tend to separate but once stirred back up they've worked find.
So, that's just my experience with grease. I'm not telling anyone else what to do, nor am I an industry trying to sell products.
Joe