OK, first thing is that the condensor is supposed to have oil in it (it accumulates there when the compressor is not running) and that oil should be replaced. Secondly, if black stuff came out, you may want to think about flushing the system (except for the compressor and receiver/drier which is replaced). The individual parts (e.g., condensor, evaporator, lines) are flushed one at a time with a solvent (terpene based) and compressed air. Thirdly, we need to know more about the leak at the hose. Is it leaking at the joint from around the threads, or from a hole/fracture in the line somewhere? If the former, make sure the threads are not mucked up and that you applied compressor oil to the O-ring. You should not replace the O-ring with a larger one, but a new one of the original size. Since you opened the system, you should automatically replace the receiver/drier and vacuum it down before adding any refridgerant. R134a?