Don't even think of putting oil on anything that ever gets near your brakes. If the brake fluid doesn't lubricated it enough to keep working, as cheap as they are, pitch it and buy a new one. Oil destroys brake parts.
Proper procedure would not have the brake fluid routed through the pump. A separate reservoir should be used.
They can dry out and not hold vacuum. A light oiling is OK in the bore.
What mechtech said, except if I remember my owner's manual correctly, it's pretty easy to disassemble and grease the seals. But I've never needed to maintain mine for about 10 years, so I'd say mine has been maintenance free.
I do remember the owner's manual, and it says it shouldn't need to be lubed, but if you do, use a silicone grease...i think it recommended silicone spray actually. A petroleum based lube will cause the seals to swell and soften, making them prone to damage.
