Leaks in the pneumatic system will cause problems with the dynamic seats and the trunk and/or door closing assist.Google+
Car Problem Reports
Mercedes-Benz SL550 Pneumatic System Leaks May Cause Problems With Seats, Trunk, and Doors
Mercedes-Benz SL550 Problem
Average Mileage: 38,070 mi (13,000 mi - 67,000 mi)
Visitor, 2008 Mercedes-Benz SL550, 20,000 mi
trunk assist failed
I have the same problem. Intermittent door lock problem -- now not working at all, trunk soft close no longer works, roof won't go down. Battery drain problems on and off for past year. I think I have a pneumatic leak causing the PSE pump to run and drain battery, and now the PSE pump motor has burned out (fuse reset no longer resets pump). :( Need to find leak, repair and also repair PSE.
Visitor, 2008 Mercedes-Benz SL550, 23,000 mi
trunk soft close not working due to pneumatic system leak,--not repaired as new unit will cost over 500
Visitor, 2008 Mercedes-Benz SL550, 42,500 mi
Trunk actuator failure..... $245 part online made of stainless steel to replace plastic part
Will go in in a day or two.... Hope it will fix .... Alert of non closing trunk
Visitor, 2008 Mercedes-Benz SL550, 67,000 mi
Trunk will not close fully, causes light on trunk assist to remain on, alarm on dash and locks not working properly.
Visitor, 2008 Mercedes-Benz SL550, 28,000 mi
New trunk latch for 817.00
Visitor, 2008 Mercedes-Benz SL550, 13,000 mi
Trunk lid would not completely close and lock thus not allowing the top to retract.
The door locks worked intermittently.
$3400 for mercedes to repair!
Visitor, 2007 Mercedes-Benz SL550, 30,000 mi
pneumatic leak with battery drain