I'm sorry to hear about your troubles with Gertie, and for sure here's hoping all will be better when you get her back, having faced extreme disappointment with my Elna, I understand your pain.
I have been using Guterman thread as well, but today I discovered the colors run, so now I will have to be very careful using up the remainder of my thread. I was considering giving Sulky a try next, I had a spool of Mettler and personally wasn't very impressed, my spool seemed to have rather a lot of lint. Ick, and I was glad when it was gone, but as we all know everyone is different and each of us had our own likes and dislikes or else we wouldn't have all these thread choices to make us crazy over.
Speaking of crazy, it must have driven you batty to hear the tensioner has been cut away by thread! That's scary!