Ta for the quick replies and advice, folks...........it may be more accurate to say that I've had the units for 11 years, but mainly over that time my work and leisure have both consisted of sitting behind a desk or a keyboard smoking ****................I doubt the actual mileage of the units differs much from the average failure stage (that's why it's kind of a bugger as well- if I had been riding regularly, they probably would have failed in warranty, or near enough to get a new set out of Shimano. After 11 years, I'm Onto Plums- the part number doesn't even get recognised on their site search!!). I did find some of the lower spec STI shifters, which are still 8 speed, nosing about on eBay today- decent enough price, and theoretically a 2004 RSX or Sora may not be that inferior to 1993 Ultegra, but I'm still wary of the design, since I came across reports of the same problem in the newer 9 speed units as well.
It looks like bar end shifters it is, then- kind of a pity, since the versatility of STI is great, but I suppose I can get used to it- bit like in them days of non-index shifting- you could usually get the gears in as smooth as silk by feel and listening once you were used to them, and since you had to take your hands off the bars to change, you either made sure you had the right gear for vertical hills, or just toughed it out......those were the days! The memories! The hernias!!.