When someone, either a non-organic chemist (as in this situation) or an organic chemist (occasionally) says simply "ether" we assume they mean diethyl ether. Purchasing the amount that will fill a capillary tube will be problematic, because that is a vanishingly tiny amount, and vendors won't want to bother. Purchasing more will also be a problem for a non-chemist, because people abuse ether in homemade drug labs. Maybe you can ask a chemist friend to let you have some. I understand its used in starter fluids, but that may not be pure, and so won't work.
I can only guess -- the oil temperature gauge won't work, because its lost its fluid. I'm wondering how -- pinhole leak, or did you disassemble it to repair it, and lost the ether as vapor? However it was lost, if you replace the tiny amount of ether, how will you seal it in? I hope you won't have to seal it with a blazed joint or something like that, ether is very flammable.