I don't know if I mentioned this without reading the whole thread again.
I never get lead on mold faces but once in a while I get some under the sprue plate or mold top. I found if you strike a wooden match and blow it right out, you can rub the lead off with the ash on the head. I don't know why it works so well and the ash will crumble of course but as long as some is left, the lead cleans right off with no harm to the mold.
I run my pot at 750° and pre heat my molds to 500° for perfect first boolits. Proper timing for each pour will keep perfect boolits flowing.
Big brass molds need a little hotter. I never figured out why that is either.
I have made one mold where I can get whiskers so I made all the rest with .002" vent lines on one face only. I cut vent lines by advancing .025" and swinging a fly cutter by hand with a special cutter I ground. No more is needed. Then I break the top edges with a small file to vent the plate.
I always use an end mill to even the tops of the blocks before I cherry and I mill the sprue plate. I leave the end mill swirls for venting. By doing that my cavities are exactly 90° to the tops.
One other thing to do with a new mold is to round off all edges and polish them, more gouges are caused by plate edges then anything except lead buildup.
But never lap a plate or mold top, you can't make it flat, been there, did that and I wind up milling again.
Just deburr the pour hole.
Making my own molds has taught me so much I can run a 20# pot to the bottom without a reject. I ladle pour and when I can't get any more lead in it, I quit for the day. Of course I always did that anyway.