Bicycle Mechanics - Shimano 105 Brifter repair

I picked up Giant roadster from about 1994; one of those carbon-fiber/alluminum jobs. Pretty decent shape, but the left brifter is wonky.
I shot it full of WD-40 and restored some clicking, but it's not "catching" on the upshifts yet.
Are these critters serviceable, or should I forget it and start haunting eBay for a new one?

They are not serviceable so you buy a new one. Roger

Or use more WD-40.....Cures cancer, I hear.

First generation STI's are readily serviceable. Remove the lever from the hood by unscrewing the set-screw holding the pivot in place, then drive the pivot out with a screwdriver. A round nut with four evenly spaced slots holds the shifter together from the backside of the lever. Remove this nut by using sharp needlenosed pliers clamped in a vise to engage two of the slots. Remove the dust cover, the return spring for the return paddle, and the return paddle shifter. Once you've done that, put a spacer of some sort back over the central post which is thick enough to take up all the slack before the threads at the top, then thread the round nut back on fingertight to the spacer. From the front, remove the faceplate with a 5mm allen key and the lever return spring will pop out along with a spacer. Thread the 5mm bolt back into its hole because a bushing may fall out later if you don't. On the backside again, remove the phillips head screw. Because you've threaded the round nut back on with the spacer, the shifter core will come out in one intact piece after you remove this screw. Loosen the round nut a little bit to put some play into the shifter internals and dunk it in some paint thinner. Use an old toothbrush to thoroughly clean the mechanism of any grease, thoroughly rinse with a high pressure hose attachment and aftersoak, and thoroughly dry. Drip some triflow into the deepest parts of the mechanism, wipe the surface clean, then brush fresh grease everywhere you can get with a small paintbrush. That's the quick and dirty way, at any rate. It really isn't all that difficult to completely take apart the shifter and reassemble, in which case you would use grease everywhere and no triflow. But that'll take at least an extra 1/2 hour. Line up each part that comes off the central post in the order in which it was removed as it will immensely help the return assembly. Clean and grease all the other parts then reassemble by reversing the disassembly. To get the lever return spring back in place engage the spring in both its holes, with the shifter cap at a 90 degree angle to its destination, then rotate it back into place. The paddle return spring is easy if you have a triple and horrible horrible horrible if you have a double. Either way, a small flathead screwdriver is the way to go. Use loctite on the round nut and the pivot set screw; you don't want this puppy coming loose on you in the middle of a ride.

I've taken one apart once, but it was a pain. I had a cable snap off within the brifter. I was able to get everything back together except the spring that holds the brake lever straight down, so the lever had a little bit of swing until it hit the spring that actually controlled the shifting. If you're mechanically savvy, go for it.

I'll play with it a bit more; I found that the cable was badly frayed and tended to catch in the frame guide, and the front DR was also extremely cruddy.
This is a 1994 bike that has likely been sitting for some years. By the look of the critter, it was not well-maintained.
Still, it's bike that retailed for about 1400.00, and I got it for nothing...

I had a 105 right brifter go bad. WD-40 didn't help. I'm cruising e-Bay now. I'm currently watching a pair of Ultegra units that are reasonable $$ so far.

I tried to no avail to repair one. I opted for the ebay route.