I was able to remedy this problem by cleaning the threads in the levers with a 6mm tap and using some new 20 length aluminum screws from this shop:
[You must be registered and logged in to see this link.]The screws seem much better quality than stock and were available in several colors.
I got 20 length instead of the stock 16, which are too short. This allows the screw to go all the way through and engage the undamaged threads at the bottom of the hole. So no helicoil re-thread required.
I had also noticed that the shifter peg was chewing up the leather on my boot when upshifting. This was solved by turning the peg to its lowest postion, so that the rubber contacts the leather on upshifts, rather than the fairly sharp edge of the aluminum hilt.
Now I just need to find the motivation to install my new flyscreen and mirrors. The short daylight this time of year makes me lazy as my dog.