UPDATE and ZE FINAL SOLUTION:

My BAS/ESP light would come on randomly it seemed, especially after going for long drives. A year ago, I decided to replace the tires since they were 10+ years old. Right rear tire had a separated belt near the center, which caused a bulge and was impossible to detect with the wheels on the car. I guess the traction control system detected one tire bigger than the others and tripped a code.

Long story short: Replaced the tires and no more BAS/ESP light. Over a year and still good.