One of my Winter maintenance items this year is to check the fluid in the steering idler (passenger side). The top is held on by 3 Allen head machine screws (#6M wrench) and has an access port in its center (13mm wrench). I changed the fluid (Castrol Hypoy C gear oil 80W-90) in Nov 2011 when I first bought the car. Upon inspection today, there was no fluid in the upper chamber, (no surprise), but the lower chamber miraculously was full. I expected to find that the majority of it would have seeped out over the past 4 years. Anyway it was cloudy, so I changed it. You can use a vacuum flush, or just a bunch of paper towels, which is what I did. Get any grey paste out of the bottom of the chamber. It is abrasive.
Note that there is an UPPER and a LOWER chamber! Just filling the unit to overflow from the exterior port is not sufficient! Pics follow.
Here's the unit:
Access port for FINAL fill:
Pull off the top and then remove this plate that is underneath. It has 4 small ball bearing spring loaded ports (2-way "valves" really) to allow lubricant to gain access to and from the bottom chambers:
This is the bottom side of this plate. You can see minor wear in the areas where the arms sweep across it:
Here is the bottom chamber, with cloudy fluid (moisture and aluminum abraded material likely the culprit):
I sopped it all out with MANY paper towels and wiped out the grey paste which results from wear of the arms. The two trapezoidal shaped arms rotate back and forth as the steering is turned. Fill the lower chamber until it is just overflowing, then put back in the middle plate with the 4 "valves" and the top.
Then fill the unit through the access port and move the steering lock to lock a few times. It is really interesting how this thing works!
Apparently the 4 ball bearing "valves" allow lubricant to flow in and out of the chambers as the bars sweep across. Makes sense as it has to go somewhere. So it flows up through the 4 ball bearing pressure release "valves" into the top chamber, which acts as a lube feed reservoir, very similarly to the brake fluid reservoir. As the arms sweep, 2 chambers are positively pressurized, while two are negatively pressurized. Thus the excess fluid is pushed up into the top chamber in two ports, and pulled back down from the top chamber by the vacuum in the other two ports.
You can watch the fluid flow past the access port and hear the air escaping under pressure as the steering is moved back and forth. I think this little thing is really quite ingenious! It provides a regulated amount of fluid to the 4 sweep arm chambers, and mixes the fluid regularly as the steering is used.
After fooling around with it for a while and contemplating the mechanics of it, top it up through the access port. It takes a few sequences to get it truly full. A cat food can, complete with plenty of greasy remnants for added lubricity, is perfect.
Pete
And the pics on the web link that Mick sent are really good! Much better than what I was able to get with the system installed in the car. 
