How do I clean up the battery leak in my flashlight?

I have a Husky rubber flashlight that uses 4 "D" batteries. The batteries are Panasonic heavy duty batteries that you can get from a 99-cents store or Dollar Tree. They've been in the flashlight for about 15 months. I decided to see how long the flashlight would stay on after replacing the bulb with a Dorcy LED. I kept the flashlight on 24/7 from October 18 to today, November 28. The amount of light was actually usable up until last night, where it was about as bright as a Maglite Solitaire.

This morning the flashlight was still on but I decided to change the batteries. I opened it up and brownish-reddish liquid poured out...maybe about a teaspoon or so.

I used paper towels to wipe some of the stuff out but what's the proper way of cleaning the flashlight? Is WD40 safe?

I searched the 'net and ended up soaking some of the parts in vinegar. Then while searching the 'net some more, I found that vinegar is for alkaline leaks, and to use baking soda for heavy duty leaks.

Would the vinegar make things worse for cleaning up a heavy duty leak?

I have a hobby tool for cleaning the battery contacts but its heartbreaking when battery gunk gets on to a reflector, Alkerline cells do worse damage, i tend to keep broken torches for parts such as reflectors when this happens.

you may have to chisel pieces out with an exacto know
i had a 2D cell maglight with some cells that leaked, i didn't know until well after i cleaned it that maglight warranties their lights with the defective batteries
i've tried backing soda and coke, still no luck.

next step i'm going to see if i can find a flap wheel or something i can put on a drill motor and reach down into the light barrel to sand the stuff out