I think when reusing limonene, it starts getting very packed full of oils and no longer remains as efficent. Then what DOES get into the solvent will be much more impure.

I did all sorts of stuff like adding 30% hcl after I'd finished salting, then giving it a good shake and discarding, then rinsing with clean water and that seems to make the limonene a little more reusable, but I don't think you get the best results unless you use fresh stuff.