I've got a 3-year-old bike with Shimano Claris (looks like ST-R2000-R) shifters. The other day, the temperature outside dropped to 40F. I took my bike out and found that I couldn't upshift the rear derailleur. I was upshifting and downshifting at random and eventually wound up with the chain on the smallest sprocket. I chalked this up to the shifter grease gumming up as mentioned here.
I'm planning on degreasing the shifter and applying some calcium grease in a few days. But in the short term, the weather's warmed up a bit and I expect the existing grease should be ok. But I'm finding that I'm still stuck on the smallest sprocket as the cable is totally slack. I can get one click of downshifting, then the lever hits some obstruction on subsequent attempts. The cable doesn't get noticeably tighter. Upshifting seems to do nothing except give me back the one click of downshifting.
Is there a stop inside the shifter that's preventing me from downshifting any more (i.e. the shifter won't let you click outside of gears 1-8)? How can I correct the cable tension, with strong preference for not removing the grip tape?