Hi,
I doubt very much that is aluminum; more likely tinned brass. But
it doesn't matter, as the capacitor is electrically leaky. The leakage
is fooling your digital meter into indicating a higher capacitance. In
reality, the capacitance hasn't changed. Take a known-good capacitor
and measure it while shunting a resistor of several megohms across it,
and watch the "capacitance" readout change.

As an aside, only Sprague made Vitamin Q caps. Lots of other makers
produced metal-cased caps with hermetic glass seals, and some of them
were junk.

73, Alan