Well done! I had to do a very similar adjustment on my Korelle. It was a bit easier because some previous owner had removed the linkage between winding and cocking. My 1/500 is also 1/100. Increasing tension just worsened the slit tapering.

I would advise to also check the collimation of the lens and screen. I had to replace the leather washer under the mount with thinner shims to achieve infinity focus, and raise the focus screen a bit to compensate… (then file the holes to reinstall the viewing hood)