Yes, AGC (auto gain control) is another way of saying ALC (auto level control)
The mic attenuator should be on but the source may still be too hot for the input on the camcorder due to AGC limitations. Local radio shop should be able to solder in a potentiometer in an aluminium box for you. Wouldn't have to cut the wires if they also used the 1/8" stereo plugs for in/out.
you might get better results if your camera has a line level input (often RCA style-jacks)