No, the problem was not my refusal to accept answers, it was my refusal to accept your interpretation of the problems. I am quite sure you provided accurate answers to the problems you posed, but they were not all the problems I wanted solved. If you had from the start identified your source for the borax you recommend and a set of specifications for it so that anyone else could search for other sources of equal product, I would have been happy. I still might have proposed a way to make cheaper product work for special occasions, who knows?
As it happens, all the impurities you have supposed might be in what I now fondly call "Mule Crap" are either very much more soluble than borax or insoluble. That includes all the likely potassium compounds. That means they may be reduced by the method I described to whatever percentage might be desired by successive solution and filtering. If you use the last solution as the product, you can dry it to powder if desired or use it as a known percentage solution. Now if I just knew the specs you require for your particular work, I could devise an engineering approach to providing it from cheap stuff and you could decide whether it is worth the trouble. I should remind you that the high quality stuff is not always available in small quantities, so you might have to buy a 50# bag to get a few ounces.