Is your negative carrier a SIRONEG or SIVONEG ?
My M601 manual shows Sironeg carrier and Sivoma 35 and Sivoma 66 masks.
My M605 manual has no name for the carrier, but indicates Sivopar masks.
I am updating my Durst parts matrix.
Too bad I wasn't in Pheonix. I would grab one of those M601s, so I can upgrade from my old M600 to a newer condenser enlarger.