My experience indicates that the unit can be locked up, by just drilling a hole through the two halves, and putting a bolt with a nylock nut through the two halves.
However I would suggest, that you spilt the unit in half, carefully checking that the rear seal has not been leaking, if you open it up and it has no oil, then of course it will not be working correctly.
The seal is a fairly common size, but again my understanding is that MB do not service it.
If you find that the seal is leaking, and you can source one, then you could put a post back on the site, for help with the oil. The oil could be a moly type. your local bearing shop should be able to assist.
Most European seals, have the size stamped usually on the inside of the seal. eg 40 x 25 x 10, being 40mm OD, 25mm bore, and 10mm width, this being a typical situation.
So before I would butcher the clutch, take a little time to find out why it does not work.
My understanding is that the fan can always be stopped by grabbing hold of it. The clue to checking it, is it turning briskly when you are at full operating temperature and car is stantionary.