Thanks to this thread, I got myself into gear and contacted Victorinox about having my Wenger knife looked at. They instructed me to go through their UK agents - Burton McCall.
This slowed things down as Burton McCall were slow to respond and misunderstood what I wanted. Eventually we agreed that I wanted blade replaced, the tip had broken, and the scissor spring replaced. I sent it off and it was ages before I heard from anyone, then Victorinox contacted me with photos of how they could re-shape the blade and a suggestion that I allow them to replace the plastic scales (the red bits). This would mean I got a new blade but loose the battered look which showed 40+ years of using the knife first as a teenager in the African bush then as soldier in the same bush and after that almost daily general use.
I decided to get the complete overall, and this is what was replaced:
The restored knife:
The new scales even contain a toothpick and tweezers.
And even better, besides the postage when I sent it off, it didn't cost me anything,
Outstanding service from Victorinox.