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Greetings:

What lubricant should I use the my convertible air tank seals? Will a light oil work?

Thanks
Gar

Can you add some detail as to what that is? Importantly, are the seals an original leather construction, or modern rubber seals?

I just verified, it is leather.

If you are speaking of the leather rod and piston seals in the vacuum top operating cylinders, I could not find any factory info on a recommended lube. You do want something not likely to gum up, oxidize or dry out. It is hard to say what might be in there which could have all of the above issues by now but vacuum pump oil has been suggested for use in other items where leather seals are used. It has also been recommended as the best substitute for the obsolete Trico vacuum oil mentioned in factory bulletins for lubricating windshield wiper motors.

Vacuum pump oil has sometimes been used on the leather piston seal in power brake units but Bendix recommended their own oil for that purpose. Pure Neatsfoot oil has been suggested as a proper replacement for Bendix oil. That would probably work for the top cylinders too but if you go with a Neatsfoot oil be sure it is the pure product. Some of the Neatsfoot oils designed for other uses have additives that enhance whatever function they are there for but can oxidize and actually cause issues with the leather over time. I don't know how well Neatsfoot oil might mix with any of the old greases that might already be in the cylinders..

Most vacuum pump oils are a fairly light weight mineral and synthetic based oil mixture which is highly refined. There are pros and cons to both types which can be obtained separately but usually a combo is general purpose and works well. If the tubing and linkage is relatively easy to disconnect it could probably be sucked up into the cylinders and distributed on both sides of the piston much like the lubrication instructions have you do for the wiper motors. It is also fairly inexpensive and readily available. There are different grades and formulations but I would stick with one of the name brands and be sure to check the label for the brand you get just to make sure there are no compatibility issues and to get the best quality oil.

For something heavier that might be applied if the unit is apart, silicone grease or one of the other water resistant synthetic greases is often suggested today for use with leather since it does not tend to dry or become as gummy as petroleum based greases.

A quick search suggests SAE 30 ND oil, oren.m.wikipedia.org/wiki/Neatsfoot_oil as HH also mentioned.