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There's no single datasheet specification for leakage current (or leakage resistance respectively time constant), because leakage is voltage and temperature dependent, and also affected by the previous charge state, each in a non-linear manner.
For an rough estimation I would refer to the below given leakage current formula from an Epcos application note. The respective time constant is 2000 s (general purpose) or 4000 s (low leakage types).
I did a google search: "al electrolytic capacitor datasheet".
I opened just the first three hits (TDK, Nichion, Panasonic) and every datasheet mentions leakage current.
It is true that leakage current depends on some parameters, therefore an exact value can't be given.
But it gives enough information to get a clue about leakage current behviour and it's expectable values.