[EC900]

Refresh the initial problem….was there an issue with the dash Brake Warning Light coming or staying on?

I had Brake Warning light come on, flicker, turn off and no adjustment could get the light to turn off, I found the contact band on the handbrake level had broken and occasionally would make contact with switch and turn the warning light on.
Second instance, sat on very steep incline and that triggered the Brake Warning to stay on. Checked the level of the fluid but it was full. Decided to flush the system, clean the reservoir and warning light turned off.

You can remove the reservoir and not introduce air, I expect the same with the two switches since they are in front of the brake lines and any air space will come to the top as was stated in previous comments.

Lastly the rubber brake lines if very old could be swollen and obstructed causing the warning light, crud accumulation in the system and old fluid with substantial moisture rusting out the switch or two.

Disregard a few comments above - I found your earlier post, I misunderstood - it’s a problem with the rear exterior Brake lights.