If you want to avoid this problem in the future, quit putting alkaline batteries in it. They all leak. Use NiMH instead, preferably a premium brand. This will be a big win, since not only will the NiMH cells not leak into your equipment, but they actually have a longer run time in higher-current equipment, such as photo strobes. The higher the current, the greater the advantage over alkaline cells, whose capacity collapses at high current. If you use the flash heavily, you will want maximum capacity (runtime). If only normal use, you will probably want a low self-discharge cell, such as Panasonic Eneloop. I've been using these since 2010 (the same cells, now 13 years old), with zero failures. They have also saved me a great deal of money over that time.
You will need a smart charger. Also, be sure not to buy name-brand but low-capacity cells. The Eneloops are 1900 mAH and are low self-discharge. No reason to go any lower than that.