PZL compass repair

I have a PZL K-13 compass that's leaking. Here's a photo of the
compass:
http://www.soarbfss.org/scgi-bin/gal...0/acc.jpg.html

This summer, I had the canopy of my ASH-26E open and it focused the sun
onto the compass and melted a hole in the front. Luckily it was in the
black painted area of the plastic, so I repaired it with some epoxy and
then repainted it. I then fully filled it with compass fluid using the
fill hole on the back.

Unfortunately, it now leaks around the circular "base" of where the the
plastic "bubble" is attached to the back. Maybe there's an O-ring seal
in there?

The back has two holes that I assume are for a spanner wrench and the
ring attaching the plastic part to the base also has some notches that
I suppose are for a special wrench as well.
I've put a pair of "c clip" pliers in the holes on the back and tried
to unscrew the outer ring by hand but it's too tight and I'm afraid to
put too much pressure on it.

Any suggestions either how to take it apart or where in the USA to send
it?

Thanks

-Tom