To the OP. I would continue down the path that you are going and eliminate everything you can before sending the KB off for a rebuild. If you do end up having it rebuild I wouldn't recommend anyone but KB.
Based on numerous "testimonials" and general bad vibes I get from KB-published PDFs I've read online, I long ago concluded that KB's customer service basically scares me (lol). "TJ" has been a great help in the past but I just generally get a bad feeling overall. I think I would be in for a real treat since I didn't buy the kit from them new but rather obtained it used.
I've got nothing but praise for Jon Bond's service, assistance and advice received to this point while I've been trying to diagnose this. Twin screw compressors are nothing if not basic and straightforward, requiring a few specialized tools to put them together. If I had them I'd do it myself. As it is I'll put my trust in JB.