Pazo

The early R129 ADS1 (Ò9/95) level controller valves are of the later “unrepairable” type. Mercedes unified the SLS controllers across model range from 1985 and replaced the earlier square type that can be rebuilt.

The self-levelling suspension (SLS) controller number on casting is often R 124 328 00 31 but part numbers indicated in EPC vary. Prices for new ones are north of 1000€!

The controller is well designed and should last the lifespan of the car. Typical issues are oil leaks and dirt. ADS1 has only a coarse plastic sieve in the oil reservoir.

Contrary to the common belief a failed valve can sometimes be resurrected. The cover (3i) is awkward to open, even if you have a 35x6mm face-pin wrench. After opening the discharge piston (3d) can be praised out from the non-return valve (3f) aperture.

Not in all but in many valves, there is a tiny bronze sinter filter in the bottom end of the piston (3q). After decades of neglected oil changes the filter tends to be clogged. You can test the filter by blowing and simultaneously pressing the discharge valve open.

Obtaining a new filter is challenging but a cheap botchery fix is to drill a small hole through it – carefully, not to damage the discharge valve behind it. This fix should be viable since early controllers had no filter. There is no easy way to tell whether a level controller has filter or not. Part numbers starting with 123 are likely w/o filter.

The discharge valve has two O-rings ~8,9x11,5x1,3 and 7x10x1,5mm. The lid seal is 44x50x3mm. The shaft has three seals but removing the control disk (3c) from shaft (3b) is difficult if not impossible. Two threads are used in unions: M12x1,0 and M10x1,0.

mahunt

This site and the other one have addressed this issue.

I seem to remember that there are some aftermarket sources that offer to rebuild the various ADS I fluid controls.

I think GUSMB has done the most for the ADS I setup. Do a search.