Hi Macman,
I have just seen this post and have had experience with some of the Motors in the past.
Depending on wattage which I believe your S5211 is the black super air clean model 2200w.
I have made a list of models which take specific type of Miele Motor depending on the control where the rewind and on/off switch is located.
MRG 42 (Twin Fan Motor) 1500 - 1600w
S300/S371 - Air Clean Plus, Jazz Plus, Meteor G,
S500/S658 Series from 99-2004 - Cat & Dog, Big Cat & Dog, Revolution 600, Solaris, Blue Moon, Medicair.
MRG 728 - 1800w
S381, S571 Super Air Clean, S718, S812 XXL 1800w ( Any Miele model which goes to 1800w takes the MRG 728
MRG 730 - Is rated at 2000w and found in the S4 and some S700 and S800 Models which are rated at 2000w
MRG 731 - Is rated at 2100w found in S748 and S848 models.
MRG 742 - Fits all 2200w S5 models.
Some of these parts are compatible with other models for e.g Using the motor and control unit from an S848 and placing on a S500/600/700 model.