The 100B schematic is here:

http://fish.shimano.com/publish/content/us/en/fishing/products/reels/reels_low_profile/curado/cu100b.SchematicPar.Single.File.tmp/cu_100b.pdf

You should take it apart again and check the part 2407. Too much to explain in writing, but you just need to make sure the metal part that runs off the thumbar is in there correctly along with whatever it touches.