The two systems are very different. The 300D system won't make any sounds. The system uses vacuum for both locking and unlocking. The SEL on the other hand uses a vacuum/pressure pump and pushes and pulls the locks.
The first system which works off of stored vacuum created by the engine vacuum pump (only on diesels and some old M110 and M115)should be able to do 4 complete cycles after the car is shut-off. It should do some cycles after sitting all night.
If it ain't broke don't fix it.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician