Renewing the hydraulic system fluid every 2-3 years or 25K miles should extend the life of many of the hydraulic system components. This is not a part of Mercedes prescribed maintenance, so most cars are still running around with the original fluid (plus years of accumulated contaminants).
Here is a proactive approach, which I believe will improve the longevity of the hydraulic system.
1) With the soft top stored and roll bar lowered remove the R129 spare tire. Under the spare tire you will find a plastic cover over the hydraulic reservoir. Remove the plastic covers three nuts with a 10 mm socket wrench.
Note: The total capacity of the system is 1.25 liters, so you should have 2.0 liters of fresh hydraulic fluid MB p/n 000989910310 or Febi-Bilstein p/n 02615 = p/n 0009899103 in order to flush the entire system. My reservoir holds 250 ml when the fluid level is between the min. and max. mark. Here is the MSDS for Febi-Bilstein 02615
rmeuropean Febi-Bilstein p/n 0009899103
autohausAZ Febi-Bilstein p/n 0009899103
Note: always check to total with shipping. Sometimes if you buy $50-$65 worth of product they knock off the shipping but you have to plan in advance to wait 7-10 days for the free ground shipping.
3) Remove the reservoir cap and approximately 250 ml. of old fluid with a rubber bulbed battery filler
then add new fluid to the reservoir so that you have about 400 ml in the reservoir. Remove the reservoir return line (tube closest to you when bending over into the trunk) with a 11 mm wrench. Place the return line into a >500 ml container.
4) Now have someone in the car. Turn the ignition key to the number two position. Lower the Soft Top. Cycle the roll bar first then the soft top
3-4 times refilling the RST reservoir to approx. 400 ml as needed between cycles. Then fill the hydraulic pump to the min/max line. Note: you will eventually see the color change to the new fluid color.
5) Replace the reservoir return line, cap, and plastic cover. Wipe up any mineral oil spillage. Return the plastic cover. Replace the spare tire and put the trunk back together in the reverse order.
I did a flush/renew of my system fluid today on 7-13-07. My car is seven years old with 30K miles.