The Hull Manufacturing company made aircraft and vehicle compasses. There are famous pictures of the Hull Streamline compass being used on WW2 jeeps, so you've just got to have one 
They're not that easy to get hold of but as usual I was lucky and found one (at a reasonable price 
) on the famous auction site. When it arrived it looked like this:
As you can see, it was in fantastic condition externally but the bulb was short of fluid (there shouldn't be a bubble in it) and the fluid was contaminated - there were all sorts of bits floating in it. So a little re-furb was required!
Taking the glass bulb from the bakelite casing was done by very gently lifting the rim with the edge of a pen knife. With gentle pressure working progressively round, the bulb came free and I could lift it out along with the brass housing.
The glass bulb unscrews form the brass housing, this took a little pentrating oil and patience but it came apart pretty easily in the end. The fluid was full of bits of old gasket, some sort of resin and smelled of a mixture of paraffin and alcohol, not the right stuff at all. Inside the housing was a flat mounting plate with a gasket on top and the main compass indicator.
So, to clean it all up I de-soldered the indicator from the plate and carefully removed it from the post. The post has a very fine balance needle on which the indicator sits so it can spin freely in the field of the magnets in the bakelite body. I was very careful not to damage that! The front of the post is painted white, this is the "lubber line" where the compass indicator is read from. The gasket was not too bad once cleaned, I think it should be replaced but I decided to re-use it (lazy!). I cleaned up all the parts, first with white spirit, then with hot water and soap. The base of the housing had been sealed with a sticky resin - I decided to replace that with silicone sealant. (If that isn't man enough, I'll use plan B - epoxy resin)
I then took the rest of the compass apart to see what was inside:
The two sets of pole magnets sit transversely for West/East and longitudinally for North South. The indicator is the compass needle which you read against the fixed lubber line - clever!
Having soldered the post back on to the plate I placed it back into the housing and sealed the back.
The proper fluid for this type of compass is ISOPAR L - a low odour, non-yellowing refined paraffin oil also known as Ritchie Compass Oil. Tricky stuff to get hold of, I got mine from West Marine (USA) via their excellent website. Delivered from North Carolina to my door in 3 days - well done!
The bulb and housing need to be assembled whilst fully submerged in the fluid, in order to exclude all the air:
Once re-filled its a matter of pushing the housing/bulb back into the bakelite body and fitting to the jeep!
Now all I need is a set of instructions on how to calibrate it, but it seems to be reading something! I also hope it doesn't start to leak, but hey, who cares, it looks bloody great right now 
For all your Jeep and Dodge needs:
Hi mate,
Just got meself one of these compasses and I need to do the same as you, so searched the net and this was the first site that came up......and you only live up the road from me, im in Fareham! how about that!!
Dont suppose you have any of that fliud left that I could buy from you??
I have some instructions if you would like a copy.
Best wishes
Paul