WD-40? Not really a lube, but will flush gunked up lube in the shifter quite well, which is a common cause of Shimano shifter problems. So flush the heck out of it, with WD-40. Work the shifter some as you do it. Do it some more. If that doesn't work, spray it full and come back in the morning and try again. If that doesn't do it, then the shifter is done. And honestly, on a 14 year old STI shifter, there's a good chance the shifter is going to be nothing but trouble anyway if it's showing these kinds of problems.