Stormin Mormon wrote, on Mon, 21 Dec 2015 18:51:00 -0500:

Wash it out with hot water. Leave
the parts disassembled over night. To dry.

As others suggested, I'd wash/dissolve the white ammonium
and zinc chloride salts away using plain water and then I'd
just let it air dry.

To (somewhat) prevent leakage in the future ... it's a good
idea to keep the relative capacities the same.

Practically, the only way to do that is to ensure the *date*
of the batteries and the *type* are as exactly matched as
you can make it.

Someone else can explain *why* that's critical. It has some
thing to do with battery-voltage reversal somehow, but I'll
let others explain it better than I can.