I feel your pain. I've had my share of serial flat episodes throughout the years. It drives me nuts. Usually I find that it is something I missed during the rush to repair it the first or second or third(!) time and not a new issue. So I end up in the home shop doing a super complete and thorough tire and rim inspection, cleaning, and tube replacement. That always does the trick but it means I have to make the time to do it properly when I might not otherwise have it. I'm grateful to have back up bikes I can jump on until I get the time.