Slimes don't spawn naturally in the caves

I've created a regular world with seed -417129829997459 and Normal difficulty, and used slime chunk finder tools for 1.8 to find the slime chunks. However, no slimes seem to spawn in slime chunks, or anywhere else on the map. I haven't tested swamp spawn conditions, but it's possible to spawn slimes using spawn eggs. They just don't show up in caves at all, no matter how long I wait. Clearing out a spawn pad in a slime chunk didn't produce any slimes either (I kept 24 blocks distance to ensure they will be able to spawn).

You can see world map here.
Attached is MCEdit analyzis of the world. Notice the complete absense of slimes.