I've read elsewhere that when replacing A/C system O rings, they should be lubed with

[Mithridates]

525 viscosity mineral oil. Does anyone know what this is, and where it can purchased? Are there any substitutes for it, if it's as rare and hard to find as your typical unicorn?

[shorod]

You should be fine to lube them with the same oil that your A/C system uses, either PAG or Ester oil. The appropriate oil should be available at most of the local auto parts stores.

-Rod