Here's some details:I'll shoot some photos of the fixes tomorrow for comparison with my initial photos on page 1.
The old nut:

Pedrazzini's refit, reusing the rest on top and adding more wood underneath:

It makes so much difference!
Old fingerboard (as provided by Geigenbau Senn 20 years ago):

Pedrazzini's fingerboard refit:

^ So smooth! A piece of art…
A major problem zone: loose saddle, as well as the end block being 1 mm higher than the lower bout, exposing a gap:

Pedrazzini's refit:

Shortening the endblock, glueing everything properly, replacing the stiff tailpiece wire with a Dyneema string.
As well as reglueing a few other problem gaps between the top and and the bouts.