For the one I used in the x5 DLA repair (China clone of Mabuchi FC-280PC-22125):
Looking at the brushes end with the connector ports up top, so it looks like a face (shaft back-end is the nose, connections at 2 and 10 o'clock, smile thing below, etc.), the connection at 2 o'clock has a red dot next to it. So I'll choose that to be positive.
Now turning the whole motor about a vertical axis 180* to look axis-on at the shaft end, when voltage is applied with the polarity specified above, the shaft spins clockwise.
So that info should safely determine polarity based on my notes of the DLA repair, since this Mabuchi motor clone is the same as the one used in that repair (I bought 4 at the same time there).
However, here comes a warning ... Since I had the stuff out, I did the exact same test on the Mabuchi clones with the 20mm shafts. Supposed to be the exact same motor, just longer shaft, but ... polarity is reversed on those!!! On those, there is no red dot, but when hooking up the same way, it spins CCW.
So, wow, I guess you can't count on anything when getting eBay China clones. They probably figure you'll just swap wires if needed and make it work.
But as I recall, in the DLA there are no wires to swap if your motor happens to be backwards from what you want. The motor plugs into pins in the assembly. So that may end up being an issue.
For me, my motor was flaky but still working well enough to confirm polarity. For you, you should be able to use my info here to figure out exactly how things are supposed to turn, and then see what happens when you put the new motors in. If it's wrong, you'll need to figure out a non-trivial way to swap polarity. Good luck!
Hey, also talking about the cold, etc., out there in WI, my son was out there for a big race today - cross country nationals. Pretty cold. No idea why anyone would choose to have a national level competition in November in Wisconsin, but that's what they did (and do a lot).
And I forgot about the pics I took - here they are, just in case my verbal description is not clear. And I drew arrows on the motor to show that it rotates CW.
