Sherry, clearly anything regarding bittul is a kulah the kashrus agencies usually don’t like to accept anymore. However, for Scotch it’s different- maybe because there are no good alternatives. I did read through the Minvchas Yitzchok (2, 27, page 57), and while he does mention many of the points you raised (avidi letaamah, bittul lechatchila), at he end he is “metzadeid lehakel”, which surprised me. He is known to be machmir as per the mesorah of the Edah Chareidis. He was not giving a definite psak though. Perhaps the kashrus agencies are relying on the fact that the penetration is halfway combined with the fact that really strong liquids like whiskey, the bittul is less (Rav Moshe mentioned this one in his teshuva), plus the fact that cleaning DOES remove some of the absorption. Finally, as the Minchas Yitzchok himself said, you aren’t tasting the sherry cask. You are tasting a smoothness caused by the sherry cask and other processes. The kid in the shul who can allegedly detect a sherried whiskey (and if he is that much of an expert on scotch, then kashrus is the least of his problems)is not tasting sherry. There are kosher sherries on the market. Taste them, and then taste the scotch, and tell me if you can detect any resemblance of it in the scotch. (The Taz says we can be somech on te’imas yisroel if it’s kosher, and the kashrus agencies say it is).
I showed your papers to my rav,who quickly looked at it and said
“He’s arguing on the biggest experts!” I do trust my rav, who’s a straight shooter, so for me the question is closed. However, I like a good controversy, Send in your work to Kashrus Magazine, the kashrus agency watchdog magazine, or to Rabbi Yudel Shain, who likes to stir the pot in the kashrus field. They will create a ra’ash which will result in the issue being addressed by all kashrus agencies.