I purchased an spd lite head assembly with cord, no battery pack, bulb,bulbsocket, or reflector. I purchased the needed parts from my LDS, and have it back together. My problem is I am unable to figure out how to disassemble the lite head to replace o-rings if necasary. I know that I could have it done, but it has been my experience that things break at the worst possible moment in the worst possible location. I need to be able to repair my equipment in the field. If you please explain how I may take this lite head apart I would appreciate it.