"Does the system still go up and down as designed. Does it raise up when the start the car and level up when a load is put on the rear of the car?"
I have not put a load in the car to test the SLS. The car never raised after starting, if it did, my understand the system is loosing pressure and SL value might be bad.
This morning, when entering the driver door, my weight, 175 lbs, cause a steel tension sound ringing. It's like a spring under tension and suddenly the tension is released is the sound I heard. Making me think a broken spring causing the sag because the engine is off and weight cause a noise. Riding to and from work noticed the car bounce up and down on a bad rut in the road. I did a lot of zip-zags at low speed and up to 40 mph and the rear end did not force the direction of the car. The car feels safe to drive.
Tomorrow will look under the car for things suggested in this thread. Thanks for the help everyone.

Bill
1981 300 TD

Before I had the level control re-adjusted in mine, it made that same sound. After it was reset by a local indy to the proper height, the sound went away.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13