Those compasses shown in the post above look like they've had hard lives.
Well, I've replaced the oil in my old Suunto compass that suddenly went green and cloudy after probably 30 years. My replacement material is "purified mineral oil" which is a totally clear liquid sold for oiling wooden kitchen chopping boards amongst other uses. It kind-of works and looks fairly non-viscous in the bottle, but it is more viscous than the old (now tinted green) oil that Suunto originally used so the dial spins slower than formerly but provides the same reading as the new compass does when it settles. These are seen alongside each other in the pasted-up image attached. But you can't put one compass close to another compass and expect to get the right reading as compasses are magnetic in order to work, so they mutually interfere. The garden table top in the photo is aluminium!
I dismantled the old compass and extracted its polystyrene (?) needle capsule. It was obvious where the manufacturer had filled it with oil as there was a tiny drilled hole in the plastic on one side which had been sealed over with model aircraft glue or similar. I drilled that out with a 1mm bit that I had to hand. Squeezing the capsule ejects the old oil easily which had quite an aromatic smell - I suspect they've mixed isopropyl alcohol or similar with neat oil to thin it down - their 'oil' was very volatile too.
I then partially filled it using a syringe fitted with a 1mm hypodermic needle , this was all I had around at the time, gave it a good shake and ejected that liquid. Then I refilled it with fresh mineral oil. This is where I discovered the green stuff had actually deposited all over the inside surface of the plastic capsule too. Despite removing most of the green gunk, a green tinge remains and is slightly fuzzy to read through the sighting lens. I could not remove the last bit of air bubble in the capsule without even more faff than I'd already had, so I just sealed it with aircraft model glue, let it set in a fridge so the liquid didn't expand and break the glue while it was setting in this hot weather we're getting right now, and finally assembled it in its aluminium housing as seen in my photo. If you try this at home, I suggest getting hold of a 0.5mm hypodermic needle to refill it after drilling say an 0.6mm hole to introduce the needle into the capsule.
So my repair has been a partial success and old compass is usable again, but the new one is so much clearer, quicker and easier to read. Suunto have improved the font for the printed scale on the dial in the last 30 years and the optical quality of the clear plastic too which are both worth having.
I could have another go at my old one sometime, perhaps trying to flush the inside of the capsule with neat iso and give it more of a good shaking, then refill it with a thinned oil, but I guess that now I've got a new one I'll simply use that and keep the old one for emergencies.
