I read a few places to stay away from Fluorescent dye in the system, but didn't find much evidence supporting this view.

I ordered, and reccomend, the Motive power bleeder, and the associated adapter hose, to test pressurizing the cooling system. There was no evidence of leaking coolant when I did this on the X, but it did lose pressure (5/lbs/hr).

I did end up ordering a new radiator regardless, since I was redoing the rest of the cooling system anyway. I'll update with a definitive slow leak test (lay on it's side, fill with water, look for spots), and some more pics. Anyone else ever have core leaks on their radiator? I've never seen this before.

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2006 e53 4.8is Imola / Cremebeige
2005 e53 3.0 Black / Truffle - AT, Sport, Premium, ZCW
2001 e39 M5 Black / Caramel - Extended Leather, Premium Audio