You paying attention to your gain on the pre for the mic?
Positioning of the mic will change the tone, more so than sensitivity.
Unless, of course, the positioning is just to far away from the source.
Try the mic on a different pre, see if you get better gain. That's if your gain isn't enough on the current pre.
I've heard of D112 diaphrams sticking... not sure of the truth to it. Mine never has, but the posted solution was to subject the mic to some high SPL to try and free up the diaphragm.
Again, don't know the truth behind it, but have heard it.