One saving grace is that most of the time (100% in my experience) it
is the R brifter that craps out so 'extra' L brifters should be around.
Post on your local club or LBS bulletin board if any for such. I have
3-4 8-9spd L brifters in my junk box.
If a drench of WD40 doesn't fix it and a cursory exam of the innards
does show a frayed cable inside the brifter or a bit of loose debris
then there is not much else to do. Cable fraying can occur around
the tight radius of the barrel inside the brifter so pull the cable and
look at it, just takes a couple of inches.
Surly CC, Raleigh Team Pro, Specialized Rockhopper
have you had a look at the shimano tech articles? I think the STI has a parts list? If you can actually get those individual parts is another story...
I recall seeing small parts for STIs at http://www.jensonusa.com
The older Ultegra STI caps would pop off and ppl would need to replace them. If you do a search on ultegra replacment caps, i'm sure it'll return online bike shops that sell small shimano parts????