I've found what I think is a safe way to clean a brass mold. I bought one of those $30 infrared thermometers which seems to be quite accurate on non shiny objects. I stripped the molds of protruding hardware and laid them flat on a piece of 3/16 steel. Using a medium flame I brought them up to 600F. I used a wood stick to hold them down and wiped the lead off with a cotton swab. A half drop of Sprue Lube or Beeswax helped the tough spots but only cotton was used for scrubbing. Shut off the heat and cool slowly. Like new, no warping.
BUT I'm still getting tinning on my mold. I'm beginning to wonder if it isn't the Alloy and will try some Rotometals #2 Alloy next. The second picture is after 200 casts. Alloy of 96/2.5/1.5 (from range scrap and locally formulated Lyman #2) was PID controlled at 650F. The MP 432256 was preheated to less than operating temp. 3 casts a minute, cut the sprue just after solidifying. Perfect fillout but the boolit wants to hang on the deposits at the end of the bands (blue arrows) And the first cavity filled has a deposit on the sprue cutter side of the top band Only.
This is my favorite mold so I'm open to spells or incantations.