Maintaining your Vehicle's Power Steering:
Power steering fluid gets contaminated over time. It gets dirty and it gets old. Believe it or not that filler cap allows dirt to get inside and create havoc inside the engine. Dirt continues to grind at bearings, seals and all other power steering related parts including hydroboosts. Being a mechanic in the US Marine Corps I had my hands greasy on a lot of vehicles. What I witnessed was interesting. Vehicles that had power steering pump filtration systems never had issues while vehicles without had issues with everything from leaking seals, to destroyed pumps, and hydroboosters. It is amazing what an ounce of prevention will do for you. If your vehicle does not have a power steering filter on it, which good chance it does not, chances are that dirt that is in there is creating some serious problems. Without a filter dirt continually recycles in the power steering system and causes extra wear which can get real expensive. If you do go with a filtration kit, be sure to install it on the return low pressure side. On the high pressure side of a power steering pump, it would create resistance and blow the filter out. Make sure you go with something that works. That or simply relace your fluid when the vehcile is serviced. I recommend changing it depending on driving conditions if you are always getting the components in dust or mud change frequently. If not I would change power steering fluids at least ever 25,000 to 50,000 miles. Don't delay especially if your vehicle is used and you don't know the history. 