Not to say you do or do not have a tube leak, but a leak at or near the end of the tube probably won't show on an eddy current test. And a leak between the tube and the endsheet won't either. That foaming discharge from the air purgers could be caused by a number of things. Since we don't know what refrigerant your chiller has, or the application (comfort? process?), or if the system has been disturbed (opened for repairs?), or what your operating pressures are (possible pump shaft seal leak), it is difficult to think of all the possibilities.