Alrighty, I'll chime in on this.
If you have the square P/S reservoir, you can't change the filter. I don't even think it has a filter. As for the fluid, don't use Dex III, my service manual does say you can use it as a replacement, but the best is to use the non-synthetic MB steering gear oil. I did mine sometime ago, and it was really dark! I recommend you buy 3 bottles since they are so cheap. Basically, use a turkey baster or a large syringe to suck out some of the old fluid from the reservoir, top it back up, start the car, turn the wheels lock to lock 2 times, and start over. Keep doing this until you finish the 1st bottle. For the 2nd bottle, since the fluid was already starting to come out very clean, I just replaced some fluid everytime I would get home. By the time I was done with the 2nd bottle, the fluid was very clean, and my P/S was much quieter. 3rd bottle is in my duct-taped bunch of emergency fluids for long distance travelling, which luckily I've never had to use yet
Now about brakes. George honestly, come on man, change your brake fluid. 1 year interval is obviously too much, 2 years is still too much, if your brake fluid delivery system is properly sealed, the brake fluid won't be absorbing moisture. I'd start replacing the brake fluid at 3 years, up to 5 years, even if it's clean. Garbage does accumulate in there, and I know that for a fact because the brake fluid wasn't changed in my car, and one day the rear calipers both seized on while on the highway, because the master cylinder was just trashed. Luckily my ABS pump survived, but my front calipers were rebuilt and my rears were replaced. Needless to say, this could all have been avoided if the brake fluid was replaced regularly. With regular fluid changes, you will never have to replace the master cylinder or the calipers, those are lifetime of the car components if the basic maintenance is done (like most other things on cars).
Now about brake fluid. DOT 4 is the best brake fluid, I'll explain why. DOT 4 has a higher boiling point than DOT 3, which is important in germany where the speed limits are non-existent, so the car's brakes can remain effective even under extreme high-speed braking. American cars have no use for this which is why they typically use DOT 3. 90's Mercedes and BMWs use DOT 4 LV (low-viscosity), for a more effective operation of the ABS pump, but if DOT 4 LV is too expensive, or cannot be obtained, DOT 4 is a viable replacement.
So let me dive a bit deeper into brake fluids. Mercedes now uses Super DOT 4, which is a kind of updated spec for DOT 4. Here things start getting a little funky. There are 2 types of super DOT 4, glycol base, and silicone base. Everything up to super DOT 4 was made from a glycol base, the lovely, deadly, poisonous main component of brake fluid. DOT 5 is exclusively silicone base, but silicone is really bad at being a brake fluid. First of all, silicone base brake fluids are often named "synthetic", which is misnomer really because not only there is no synthesis involved in making brake fluid, there was also never a petroleum-based brake fluid, glycol has nothing to do with oil. I suppose they name it so because it is not the "conventional" glycol based fluid, but anyway, I digress. So what's the real reason silicone is bad at being a brake fluid? Silicone absorbs air, but doesn't absorb moisture. Which means that inevitably, silicone based fluids in brake lines will make the brakes feel spongy, as if there was air in the system. This makes silicone based brake fluids a little bit easier on maintenance, because there can still be some air trapped inside the system and it still provide adequate functionality, but the only way to flush out the dissolved air in the system is to do a brake fluid flush, which must be done regularly. However, if any moisture gets into the system, things start to go bad very quickly.
Now, glycol based fluids are better because they do the opposite, they don't absorb air, but they do absorb moisture. So glycol based fluids can take a little bit more abuse from being exposed to the elements, but as soon as a little bit of air gets into the system, your brakes become very ineffective. However, like all things, glycol has a limit to how much water it can dissolve. Once it is saturated, you run the risk of having water sloshing around in the brake lines, which could corrode them. Now I know that corrosion has occasionally a useful purpose (such as protecting aluminium), but it has no business in your brakes lines, calipers, master cylinder or ABS pump.
So, in summary, change your power steering fluid, change your brake fluid. If you have any concerns about the chemistry involved inside the various systems of cars, ask me.