I ran a 27t monster stock motor in a 1 1/2 hour enduro with no problems .. didnt have to change brushes or anything until after the race ... com looked very good .. just make sure your gearing is right . and have fun ..
I also ran an enduro with a monster stock, about 4 1/2 hours, well over 1000 laps of continual running. Motor came up to temp and stayed there, but never over heated since we had it geared right. We used 4499 brushes, and they still had serrations afterward.
One issue I think is to make those Tamiya motors move the car at a reasonable speed they need to be massively over geared. Try a real motor and your problem will go away.