Ok battery "leaks" come from one of two places (well one place and one large group of "other") The Filler cap. and everywhere else.
If anywhere else. Replacement is indicated. IF the battery is a GC-2 or like six volt then it is 1/2 of a 12 volt battery (You two sixes in series become one big 12) replace BOTH halves.
If it is from the cap:
I have read many say "fill with DISTILLED WATER" to the bottom of the filler tube. THIS IS WRONG!!!!!
1/8 to 1/4 inch BELOW the tube (1/8 if fully charged if not go for 1/2 then charge and try again) WHY.. Well you are looking at why.. It needs that eighth of an inch gap.