Since you're posting in the Sea & Sea section, I assume it's a Sea & Sea housing. My D300 housing has a similar issue with the metering adjustment wheel. The control on the camera is stiff and the wheel slips. I took it in to Backscatter in Monterey and they suggested putting a little tape on the control to tighten it up. The other alternative would be to take it in for servicing and they could probably replace the rubber wheel. Since you're in New England, Backscatter East in Derry, NH might be of help.
I think a little double-stick tape might suffice, though. Also, as suggested by acrofrag, there can be wear on the camera mounts. I've been stupid in the past and forgotten to take the eyepiece off or lock down the tray when installing the camera or things like that and it's amazing what doesn't work due to a little extra pressure tilting the camera. Check for any play in the camera when locked down on the tray and see if things can be adjusted a bit and retightened. Sometimes a little shimming of mounting points might work wonders.