I honestly have to ask, the water break in is still a thing? I haven't bought a new brushed motor in probably 5 years or so.
I just picked up a Spektrum Firma rebuildable brushed motor. It looks just like many others out there. I'll see how it does long term.
I broke it in using a small AA battery.
In the past I have used the distilled water method with mixed results.
Personally, well ones that I did in distilled water and then oiled ran faster, they also seemed to burn up quicker (brushes, comm wear, etc).
I don't know if it's just me or if I am doing something wrong. Perhaps bad luck.
I can distinctly remember back in the day breaking in a few nice brushed motors just to have them seemingly burn up and being quite irritated by it.
Listening to the motor connected to the AA sounds similar to it running in a cup of water to me.
You can hear the motor start to ramp up a bit as the brushes break in. And with no load on it, it's nice and easy. *Fingers crossed* it's gonna last.
If not, it was a cheapo this time.