Glad you included the

smilie.
Oil filled caps sealed in metal cans may last indefinitely, but not the ones in paper, or even the black beauty types. Oil absorbs water too and the paper will degrade then.
I had a very large HV cap that I wanted to do some scary experiments with and it had been drained of oil. Before filling it with mineral oil I heated the oil to drive off the water. It was amazing how much water came out. After all, oil and water aren't usually thought of as mixing, but there is some solubility.
John