The following is from Steve Brotherton's reply to my post about my steering box:
Next time you are filling it open the bleeder on top of the steering gearbox. If done with engine off till fluid comes out and full the system will need little bleeding.
If bleeding is necessary, I hook a section of MB hard vacuum line, with a rubber hose to couple, to the bleeder, open the bleeder and place the other end into the reservoir. Start the motor but **DO NOT** turn the steering wheel (you will blast the line off and throw fluid everywhere). The fluid will give up its air and clear fluid will flow through this into the reservoir.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
If you cannot locate the bleeder valve, you can try letting the engine idle and allow the pump to purge itself, while continually topping off the resevoir. If using Steve's method, as he said, DO NOT turn the wheel.
Next you'll have to figure out where the air is coming from. Either a leak in the pump seals or one of the lines, sucking in air, or maybe at the steering box causing as slow fluid loss. Once the fluid level drops, when you turn (left I think) the level will temporarily drop further, and the pump will put air through the system.
73 280 SEL 4.5