Probably just a cap to keep crap from getting into the bushing at the end.

Go to the binaries group he referenced and look at the photo. It's not over
the ball bearing, but closes some kind of drilling or such, next to the
bearing.

Does it feel like there's something within/underneath the "red rubbery"
substance? Or is it just a rubber plug?

From the photos it looks like it simply keeps that capillary closed. I'd make
sure it stayed closed. If yo want to expose the end of this motor, you might
replace it with a threaded hex plug or such. But that requires drilling and
tapping the hole, which introduces other contaminants. Maybe just silicon
sealer in place of the plug?

Good luck,