Renewing the hydraulic system fluid every 25K miles or every 2 years 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
Note:
rmeuropean Febi-Bilstein p/n 0009899103 for $7.75/Liter
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 12 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.
Cycle the soft top and roll bar 4-5 times and refill the 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. My car is seven years old with 30K miles. I tested the pH of the old and new fluid. Both read the same at about pH 5.5. I did this because I thought that the pH may have changed over time and could contribute to the degredation of the seals. I did not find that to be the case. But if you look at the attached pictures you will notice a color difference. The old fluid (left vial) looks like a beer color while the new Febi-Bilstein 02615 fluid (right vial) is clear. I have also attached a picture of my hydraulic reservoir with the old fluid.
