Q: I put a small amount of power-steering fluid into the brake-fluid container of my car by mistake. Please let me know whether it would cause any problem with my brake system and what I should do to correct it.

A: Most brake fluid is glycol-based — the exception being silicone brake fluids used in some high-performance vehicles — and power-steering fluid is petroleum-based. They are not compatible. Exposure to petroleum products can cause rubber brake components to swell, leading to potentially serious problems.

In cases where contamination has just occurred, the brake system needs to be completely drained, flushed with denatured alcohol, refilled and bled with the proper brake fluid. In this case, quickly siphoning the master cylinder reservoir may remove most of the power steering fluid.

If contamination has spread throughout the hydraulic system, you’ll have to replace or rebuild major brake components, including the antilock braking system’s hydraulic control unit.

Q: I have a 2003 Hyundai XG350 with 80,000 miles. In the past six months, I have noticed some clunking in the automatic shifting when I accelerate to about 20 mph. It will happen in winter and summer, unless I accelerate quickly or unless I let the car warm up a bit.

A: The dealer’s service computer can check for transmission fault codes and perform sophisticated diagnostics on the quality of each upshift. It may be possible to reprogram the adaptive values in the transmission control module.

It’s also worth checking both front-drive axles and their constant-velocity joints along with the engine/transaxle mounts for wear and play.