1.4.2.8. 60 Newtons? To fire the seat by pushing the handle forward. Is that broadly similar to a force of 60kg? 75% of his bodyweight? (I know about force and mass etc, but broadly speaking for the man in the street)
60 Newtons is roughly (just over) 6kg under (Earth's) gravity. Not much, in other words.
(Newtons (N) = Mass (kg) x force, or acceleration if you will (G, or m/s2))
G being equal to ~9.8 m/s2 on Earth
Lastly from me for the moment. If the seat was unsafe for 4 days, (unless I have missed it) the investigators have failed to document every event that happened between then and the accident. It seems to me that ejection seat pin checks up to this accident may have been a cursory glance, but I would therefore make a distinction of (an engineer) leaning into the cockpit to check something, or to actually sit in the seat.
Unfortunately, if one accepts that 'the boffins' are correct, we probably know
how the chain of events unfolded, but are unlikely to know
why, to anything approaching 100% certainty anyway.