Dura-Ace ST-7900 won't downshift

[rasmusic]

My left ST-7900 suddently won't downshift properly. I can shift upwards as much as I want, but when I press the downshift lever nothing happens if I don't manually press down the small part with the pink arrow in the middle of the first photo. After pressing it down (like seen on the second photo) it works fine UNTIL i upshift next time. Any ideas? A dead spring? If so, can it be replaced?

[Rush]

WD40 blown through my old STi shifters helps downshifting. I presume your ratchet mechanism is lightly lubricated.

Just to be sure, by 'downshifting' you are referring to letting out cable thereby releasing cable tension at the derailleur, and moving to the smaller cassette cogs...correct?

[rasmusic]

Yeah, that's what I mean. Isn't "downshift" the correct word?

I've already tried the WD40 trick, but it didn't work. Any other ideas? Is there any replaceable springs in there?

[Guerdi]

I have had exactly the same problem last fall and I couldn't fix it unfortunately. I had to buy another lever.