Help needed with Bongo 4

Hi guys, new here. I have some problems with my old Bongo. The guitar had sat in storeage for a few years. I got it out recently and realised (embarrassingly)I had left a pair of 9v in the slots. I replaced the old batteries the other day and fired it up and it “seemed” fine. Went to play it today it was back in its case the whole time, and the new batteries were dead. I have just unscrewed the back plate, then the battery socket and gently eased it out. It appears that one of the batteries had released its alkaline a formed a blue crust under the copper tabs. Also the black and red wires came away, battery fluid must have weakened the joint. Thats not a big problem, as I can solder ok.

1. I plan de-solder the battery cannister and give it good clean out.
My questions are what are best cleaning products for this kind..i have wd40 contact cleaner. Is there something i should use for battery fluid before hitting with contact cleaner.

2. Also if its beyond repair, and the battery cannister is dead, where can I order a replacement part?

3. If I clean it and re-solder the wires and battery drain is still happening. What else would you normally check/do?

Going back a few years but I suspected that batteries seemed to drain faster than normal. Seemed like every time i took it band practice i would need. Probably why it went into went into storeage.
Its a beautifull playing and sounding guitar, I want to get it sorted.
Cheers
Steve