I have 3-4 yr brushless (BLDC) still running smoothly on my other RC models and quads. I don't ever lube them as lube attract dirt to the shafts, even in small quantities. These are high-rpm, shielded bearings (not sealed, shielded means less friction but small particles can get inside and it may need maintenance).
Problem is, oil won't stay there with all the spinning and heat. It may break down and get contaminated too. I don't lube my flying models ever, but I do use Finish Line Electronic Cleaner/lube (for MTB and road electronic shifting groups) here and there on occasion, even the gimbals. If you're going for it then clean everything first, and beware: these are sensitive things with very small parts and if misaligned or under any load upon reinstallation, THEN you may get into trouble at some point with your motors.
RC Cars suffer a lot for being close to the ground and stuff but we have ways to deal with it, different motors and protection, etc. ACs are OK because they fly, just avoid crashes, sand and dirt as best you can, if dust comes in then blow with compressed air and check for spin. That's all I do. These bearings usually last yrs without maintenance, DJI is not top stuff but their parts are good quality overall.
I have 4 backup motors for my P3Ps but there still packed. After hundreds of hours and flights (my 1st P3P has ˜ 400 flights) the originals are fine. I've seen more ESC failing than motors in fact, but it's good practice to keep an eye on motors. If it ain't broken don't mess with it. But if you feel any of your motors is weird in some way ("play" at the shaft, not spinning smoothly, something inside, etc), take it to DJI or RC shop for a pro check.