W210 ABS BAS ESP indicators came on while driving
 

In my 98 E300, the ABS, BAS, and ESP indicators came on driving (I believe while turning a corner), as is the case when the battery is disconnected. I turned off the car, turned it on, and the indicators came on immediately. Turned car off and on again, turned the steering wheel all the way in both directions and the problem went away.

What, if anything, can I conclude from those symptoms? Brake light switch?

If it was neutralizing steering sensor then you resolved that when you turned steering lock to lock. Without a puter it is kinda hard to tell what is going on. If it was not neutralizing then it will pop back up. Has the battery been disconnected recently?

the brake lamp switch failure shows up the indicators right on pressing the brake pedal while driving.

If you had it while turning, its most probably the steering angle sensor which you reset again.

Battery not recently disconnected.

If it is the steering angle sensor, was this probably just a "glitch?" Or is it likely starting to fail?

Start with easy bits first, brown earth clamps under hood, from memory there are 4/5, then brake switch as mentioned.

ABS speed sensors also cause the same issue as they lose their magnetic field over time. Reluctor rings on the back rust out and snap which can be hard to see or detect as they still look whole.

Hi shertex did you ever resolve the issues?