Q We own a 2001 GMC Yukon XL with 221,000 miles on it. Last week, we took it to the dealer because the check-engine light had been on since shortly after the last oil change. They put it on their diagnostic machine. A smoke test identified a small evaporative leak from a small crack on a vacuum connection on the fuel tank. They said we would need a new ($1,436) or used ($860) fuel tank assembly. They asked if we could smell gas, and we said no. Is it dangerous to drive the vehicle like this, and is it worth fixing considering the age of the vehicle and the price of the repair?

A Ask the dealer for the precise diagnostic trouble code that triggered the check engine light. The evaporative emissions system, or "evap" system, like all computer-controlled systems on modern automobiles, has sophisticated built in self-diagnostic capabilities which can pinpoint the problem. Probably the most common code for emissions system failures is P0446, indicating vacuum levels and loss rate in the evap system are outside operational parameters. The most common causes for this are a bad fuel cap, leaking evap vacuum lines and/or damaged vapor canister or valve.

Considering the age of the vehicle, plus the fact that the leak is vacuum rather than fuel, I'd try to fix the leak first. Replacing the damaged section of vacuum pipe with a high-quality section of vacuum hose and hose clamps might be a workable repair.

Q I recently purchased an '04 Audi A6. Now, the power steering is making noise. I have had to park on hills at times and was told parking with the wheels turned could put extra stress on the power steering. Is that true?

Replacing the power steering pump is very expensive. Are there any additives that would help? Or should I suck it up and put the repair on my credit card?

A Parking on a hill with the front wheels turned so that the vehicle is somewhat "leaning" on the steering system cannot influence the power steering pump in any way. Since the engine is not running, there is no hydraulic pressure being generated nor any fluid circulating.

More to the point, Audi issued a service bulletin for precisely this complaint: noisy power steering. My Alldata automotive database pulled up bulletin 48 10 01, dated January 2010, that suggests checking the fluid level and filter screen and looking for air bubbles in the fluid one minute after shutting the engine off fully warmed up. If no air bubbles are present under this condition, air trapped in the system is not the problem. Try adding two ounces of SeaFoam Trans-Tune to the reservoir.

Also, make sure the reservoir is properly topped up with fluid. When the engine is cold, the fluid level must be at the "MAX" mark. When fully warmed up, it should be 10mm above that mark.

Q We have a 2004 Toyota 4Runner and a 2005 Chevy Silverado with the same problem: thousands of tiny chips in their windshields. These chips are so small that they cannot be seen in normal conditions, but when the bright sun hits the windshield at the proper angle, thousands of sparkling light points explode on the windshield. This effect can be blinding and lasts only for seconds when the sun strike occurs. Short of replacing the windshields, is there a method by which these tiny imperfections can be buffed out?

A I'm not aware of an effective way to buff or polish glass to remove these imperfections, but a coat of automotive wax will help minimize that sparkle effect. Because of the safety issue you identify, if you have comprehensive coverage, check your auto insurance policy. Windshield replacement for damage generally will not raise your rates and may be covered at a low or zero deductible.