John, congrats on finally getting these rifles worked out. A Mannlicher-Schoenauer is a fine-tuned instrument to be cherished.

The non-working DST is probably just out of adjustment. If it won't set, carefully back out the adjustment screw by increments until it will set. Once you establish that, back it out a little more and set it. Then slowly turn the adjustment screw in until the trigger releases. At that point back out the adjustment screw 1/4 to 1/2 turn and it will be in adjustment.

Good luck!

Curl