Cleaning the casks reduces the amount of absorption in the cask.
Rav Moshe’s use of the pri megadim’s pesicha shows us that “avida letaama” is not the same thing as “kiyuha”- when it’s a very weak taste it doesn’t count as a taste. It sounds like from his teshuva that wine is different from other Chana”n in that once the wine is diluted past 1:6, it IS NO LONGER WINE. So even if the sherry cask is less than 1 in six, once they blend it with other non-sherry cask scotch casks it would no longer be wine, at least lefi Rav Moshe ZT”L. However, according to the bittul beshishim crowd (who say we follow the shach over the Tashbeitz it would seem that your research is me’orer a shaila. I printed it out and will show it to my rav. I also emailed it to a relative who is a mashgiach for a kashrus agency. I asked my rav on Shabbos and he was dismissive of anything changing in the world of scotch. Ein ledayan ela ma she’einav ro’os, so I will show him your magnum opus, and until then, Yishtu ashirim veyishkaru.