It would be helpful to know which Magneto you have. A quick way to tell is:
1. If you can't install the battery from the bottom, venting is out the bottom and you don't have a floating 510 pin, you have v1 of the original Magneto.
2. If you can't install the battery from the bottom, venting is out two holes on the tube with one on each side and you have a floating 510 pin, you have v2 of the original Magneto.
3. If you can install the battery from the bottom (i.e. you have a self contained button assembly that does not block the tube), venting is out three holes on the side of the tube and you have a floating 510 you have a Magneto II.
Any chance you can upload a picture? If you have the original Magneto, the button assembly was known to be problematic with the retention ring coming loose.
EDIT: Edited to correct venting on v2 model.