Byrd's instructions for installing a Shelix on a DW735 indicate removing the knives as the 3rd or 4th step in removing the original head. No mention...
Mattress bag is a good thought--but since Derek doesn't have one, maybe check with a local furniture or mattress store for something they take off a...
On my TS (not a PM 1000), the lock knob compresses a fiber washer to secure the lock. Age, compression, dust, whatever renders the fiber washer less...