One of the most frustrating things in dealing with machines is when two things happen at about the same time but are not related.... I suspect this to be the case just like Jim says....
However, you should also check to see if you have any algae indications... are you using a clear 90 degree inline filter ?
Also, if you have not been good about the coolant system, or the car is really old ( and yours is )...then I suggest at the same time you pull the radiator and clean it that you pull the core plugs ( freeze plugs ) and use a 90 degree tip on a pressure washer to flush everything out of the coolant passages ,,,, do it untill they run clear water... parts of the block always have places where the coolant flow is less than others.... and just like bends in the river are where the gold nuggets get deposited.... stuff accumulates from the rest of the block into cavities in those areas....
Too often on these old Mercedes blocks people do rebuilds without taking everything apart and having the block VATTED.... so at some point this catches up with some owner with lessened thermal capacity of the coolant to take heat to the radiator...