Topic

I have a 2000 F with much the same millage as yours, my spheres were shot.
I would go down the route of getting the valve inserted and regased which I did, so far so good,or the Mike Satur replacement kit, more expensive but a good permanent solution.
Due to the age of the second hand spheres you may well be throwing good money after bad buying second hand.

I am sure there is plenty of advice here as most F owners have by now had problems with spheres.

If I hadn't gone for TF subrames I would be looking at the valve replacement spheres rather than second hand.
Before going TF I had replaced 3 spheres with used ones and they weren't any better in the long run.