Looks like you have a dilemma... Did you ever isolate the issue with the first pair. Are the wires frayed? That can happen after years of handling. You did the first thing I would think of, try the mics with different recorders to isolate if it's the mics or not. Any chance you have access to a DR-2d or another 4 track recorder? If your situation is that urgent you could do a 4 track and combine the channels properly in post, but that's a worst case scenario. Just an idea.