Interestingly enough, the hammer spring was lightened to a Wolfe ten pound spring and worked fine (zero misfires for 400 rounds or so). Then it started missing about two in a hundred using the same Remington 125 HP 38 Spec rounds.
I moved back up a bit to the 12 pound spring but I am still missing on about 2%.
I have added hammer shims because I was seeing contact marks on the left side of the hammer. even with the hammer shims the hammer is still dragging slightly on the left side. I wondered if the hammer spring strut might be pushing the hammer slightly off center as it cammed forward, but everything in the strut pocket of the hammer looks clean.