Hey everyone, need some help; i know coolant leaks are common on on E39's, done a lot of reading here and i'm still coming up empty. I have 2002 540i M sport 6 gear, 154000 kms (95 miles); car has been going down on a coolant, not a huge amount, about a cup every two weeks. Pressure tested system, found a crack in the rad; replaced rad and tank. Started driving the car again, still going down on coolant. Pressure tested system, didn't drop any at 15 psi for an hour. No external leaks, nothing on the driveway. Put dye in the system, drove the car for a day, looked high and low, nothing. Should I be suspecting a poss head gasket? No smoke, car runs like a champ with good power,no codes, not overheating....completely stumped. Suggestions???