wk2000...
You said that you made the O-ring for the mag-lite head from O-ring stock. I've done this before myself and have had mixed results. It's difficult to get the measurement right when making an O-ring that fits on the inside of something. It usually turns out just a little to small to seal properly. The O-ring must be large enough to seal against the outside walls of the reflector housing as well as the lens and bulb. Also make sure that the mating ends are perfectly aligned and that there is no excess glue squeezed out. This is critical as misaligned ends will allow water past the O-ring and the excess glue forms a ridge that will do the same thing. My suggestion is to go to a hardware store in the area and try to match up an O-ring with the mag-lite. I did this and found an O-ring that fit perfectly and has worked flawlessly every time. If the O-ring just drops into the top of the mag-lite then it's probably to small, it should be just a hair to large to just drop in and therefore will need to be pushed into the reflector housing as the retaining ring is screwed down forming a nice tight seal. Make sure to take the light head along with you to check the fit. The retainer ring should screw all the way down on the reflector housing just like it did on the flash light before it was modified. Also look at the front of the light head when everything is in place and assembled. There should be a nice black ring all the way around the glass lens indicating that the O-ring is sealed against the lens.
As for the Sealcon fitting leaking, you said that you installed an O-ring under the base before it was installed in the light head end cap but did you counter sink the surface of the end cap to allow the O-ring to seal and not be squeezed out? this is very important as it gives the O-ring something to seal against on the sides. If you don't counter sink the area around the hole it will usually leak regaurdless of how much thread tape you use.
If you're worried about the material thickness of the end cap and how it will hold I'd suggest filling the end cap with JB Weld first and then drilling and tapping the entire thing. That will give you a nice thick surface to tap and for the threads of the fitting to screw into. If you've already drilled the end cap just put a bit of tape over the hole before you fill it.
The Acrylic is a PITA to cut. It melts very easy so as you're cutting it the heat from the saw blade melts the stuff and causes the blade to stick. I found it was easier to cut the stuff with a hand saw as close to the shape I needed as possible and then, using a disk sander, sand it to the final shape.
Good luck and let us know how things work out.
