When I saw John's question today, I thought of my mold reclaim project for today. I offer this as a similar situation and how it was solved.
Today's Project; reclaim a NOE brass four-cavity mold. The bullets are .002+ out-of-round and the tow inner cavities have fins varying in size with each fill. When you close the empty mold and hold to the light, there is strong light shining through. I am not sure how this happened, my thought is the usage caused warping or it was dropped.
First step: Try different handles. RCBS, NOE and Lee were tried with the exact same result. The handles are not the problem.
Second step: Clean the faces. There is trace lead at the bottom of the two inner cavities. Heat and bronze wool, scrub along the vent lines. No change, the light coming through does not lessen. When held to the light, the sunlight came streaming through.
Third step: Check inner faces for flatness. Not having a surface table, I set them in a vise and used a (new) flat file to dress the surface. There was a few high spots on the first and second pass. However, on the third stroke the mold surface was slightly touched across the face on both inner surfaces. I moved the alignment pins back flush with their surface such that the file had a clean sweep across the surface. This time, the sunlight was blocked across the entire mold. Major change.
Fourth step: Reset the alignment pins. The mold was set on an inch-thick brass piece to allow structured hammering. (I have done this before with iron molds and a person can hear a different tone when the alignment pin first hits the alignment hole.) First I marked the alignment holes with a red Sharpie to have witness marks and see the contact points as the pins moved forward. Next, the pins were driven with medium hammer blows to see how far the pins would move. After eighteen blows, the pins went in the alignment holes, the witness marks showed they were even. And these blows sounded different.
Fifth step: Use the mold. The mold was back to its flawless behavior; no fins, out-of-roundness within .001. bullets drop easily from the mold. The alignment pins are tight, there should be no movement. However, I will check this mold each time it is used for alignment and pin migration either forward or backward.
Farm boy from Western Illinois, living in the Magical Pacific Northwest