I think you'll have to contact Plastimo
Until recently, most compasses used Odourless Mineral Spirits as their damping fluid.
Ritchie (for one) now uses a fluid called Isopar L ® (*1) that has similar properties, but with some added benefits over Odourless Mineral Spirits. The two can be mixed together.
(*1) Isopar L® is a Registered Trademark of Exxon Mobil Corporation - generically known as: Isoparaffinic hydrocarbons (Isoparaffin), Hydroheated heavy naphtha (petroleum).
Some compasses are filled with mineral oil
. Baby oil
is mineral oil, although it often has other additives, like perfumes.
Some older style (up to 1960's) Compasses used an Isopropyl Alcohol and water
mix, or Kerosene.
See the (unhelpful) PLASTIMO FAQ:
➥ Plastimo: boat equipment – FAQ - Technical support