I'll throw one more log on the fire. The source of the 96/2/2 alloy isn't mentioned. There is the possibility that the alloy batch (or a dirty casting pot) is producing boolits with nasty contaminants (not necessarily visible) that can aggravate leading. Be sure the alloy is clean (well fluxed) before casting. If contaminants are part of the problem, try casting/fluxing at a higher temperature to force the crud (aluminum, zinc, silicon, etc) into the dross.