I haven't balanced my motors, pulled them out or oiled a bearing. i've had 30 flights now, totalling about 200 minutes, a few hard landings and I'm on my third set of props. I balance the props on a dubro and check the IMU after each flying session, it usually requires a software basic calibration each time.
Tonight I ran the quad in my house, in ATTI, with a fresh battery at a low setting, not enough to lift, until it ran the battery down to red lights flashing. That took 45 minutes, and the battery was at 10.7 volts on my voltmeter. Was nice having the fan effect except for dust bunnies blowing around! I immediately checked the four motors for temperature with a point and shoot temperature sensor that measures a spot 1 cm in size. The outside of the motors were 28c plus or minus .5c, ambient temp was 22c. The coils in the motors all were around 30c plus or minus .5c. Each motor was slightly different, a degree or so, but because this was done in my house they should all pretty close. Not a lot of variation.
I've read in these forums that if one motor feels warm it may be about to fail from bearings etc. The Thermohawk 420 thermometer pen is about $40 on ebay and is a lot better and faster than guessing with your fingers which is warmer. Its also useful for checking out sick kids or hot spots in car engines! So i'm assuming all is well and I dont need to oil/balance/replace anything. yet! I'd be interested in others experience about why you changed out the motors or what maintenance you do on them.