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Q: I have a 2014 Subaru Forester with 32,000 miles. At a recent dealer service they said at 30,000 miles I should have the brake fluid changed. I refused, but looked in my owner's manual and, sure enough, it calls for the brake fluid to be changed every 30,000 miles. Never heard of such a program — what do you know about this?

A: I know that having brake fluid changed every two years or 30,000 miles is a very worthwhile maintenance service. I'm always amazed at the condition of the brake fluid I find in most vehicles — nasty, muddy-colored brown. New brake fluid is virtually clear.

The ugly fluid is the result of moisture and corrosion contaminating the hydraulic system. Brake fluid is a glycol-based fluid that is hygroscopic, meaning it will absorb moisture from the atmosphere. Moisture contacting iron and steel components leads to rust — exactly what accumulates in brake fluid over years and miles of operation. Remarkably, in most cases these contaminated brake systems still function.

Thus the need to perform periodic brake fluid changes. The simplest short-term method is to use a turkey baster or similar siphon device to draw down the master cylinder reservoir until nearly empty, then refill it with fresh brake fluid. Granted, this does not fully exchange the fluid in the system, but does replace a significant percentage of it. Doing this every year at very little cost will reduce corrosion build-up in the fluid.

To replace 100 percent of the brake fluid, the brakes need to be bled until fresh, and clean fluid is seen in the bleed hose at each caliper/wheel cylinder. This method also flushes moisture and debris from the system.

Silicone-based fluids like DOT 5 brake fluid do not absorb moisture and have been the choice of racers for years due to its non-hygroscopic characteristics and resulting higher boiling point (even the smallest amount of moisture absorbed into glycol brake fluid significantly lowers its boiling point). Silicone brake fluid is not compatible with glycol-based brake fluid so switching to DOT 5 fluid would require a complete flush to remove all traces of DOT 3 or DOT 4 fluids.

Q: My son-in-law is experiencing weird problems with his 2007 GMC Denali. While driving, the door locks go up and down, the headlights dim and go bright and the vehicle will not turn off. He took the car to a dealer and after running a diagnostic check, they charged him $221 and said they didn't know what the problem is. Now a mechanic friend of my son-in-law is going to replace the windshield, as he suspects water is getting in somewhere and causing the problem. The problems I described all happen occasionally but, as you can imagine, are stressful.

A: Don't replace the windshield yet! I found several technical service bulletins and a recall notice in my ALLDATA automotive database that address bizarre electrical issues similar to what you've described.

The bulletins and recall, including NHTSA recall 08V441000, point to a potential short circuit on the printed circuit board that controls the heated washer fluid system. This issue can affect other electrical systems in the vehicle, including those you described. I'm surprised the dealer didn't check for this because of the potential (although slight) risk of overheating and fire. I suggest having the dealer check for this problem.

Q: I have a peculiar situation with our 2009 Hummer H3T. The power steering fluid is very low and at one time it was up where it should be, yet there is no leak anywhere. I checked underneath and the steering column and it's all dry. Any suggestions?

A: Look again. The fluid has to be going somewhere. If the end seals of the steering rack leak fluid may accumulate in the boots covering the inner tie-rod ends.

Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.