On my AirRaid CAI I had to put a new O-ring on the sensor, since I broke the blue one taking it out of the stock tubes. I also had to remove one of the wiring clips to give me more slack, and re-rout the wires slightly to allow enough length to connect. May be worth a shot.
When I installed the sensor, I put a dot of oil, from the oil fill lid, on the O-ring, then put a flat head sensor in the slot on the sensor and pushed down , once I heard it go into place, I connected everything up. Once it is in place it should be almost impossible to remove again. The AirRaid also has a small screw and washer that holds it in, in place of the factory screw in/click in stub. Does the MDesign not have that?