The reason those fan clutches were leaking is because they must be stored upright or else they will leak fluid. However, in your overheating case, I'd suspect a bad water pump or else a bad radiator. Start by replacing the thermostat first. If that doesn't help, try the water pump next. If it still overheats, then you might be looking at a radiator. If you do have to put a radiator in, then make sure you go with the original metal MB/Behr radiator, not the plastic ones. The metal ones are much more expensive, but well worth it.
'67 250SE Cabriolet
'93 300E 2.8