I thought so... I'd rather not use citric acid this time, though. Would Purple Power be a good choice, or should I use something else? (someone suggested dish washing soup... I don't know about that...)

So, how do you suggest I cycle it? How many times just tap water, how many times (Purple Power), and what ratio water/degreaser?
Also, can I do it with the fan off (car stationary), and how long to keep the engine running each time? My idea is to keep it running shortly each time (given the leak) but long enough to do some actual cleansing. Does anyone know how long it takes for the liquid in the cooling system to circulate fully with the engine running slightly faster than idle speed? (Of course, when the new radiator is on, I would also do a few full force flushes) How hot should I let the car get, in this particular situation?

Much appreciated...

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1979 240D, W123, 105K miles, stick, white w/ tan interior.