I think my front shifter (Shimano 105 mechanical) needs to be degunked (is that even a word?). What degreaser and lubricant do people recommend? Would not want to damage and/or eat into the plastic/rubber bits. Thanks.

One Step is a pretty good choice. Figure out a way to get the lube in there and flood it.

https://www.amazon.com/Finish-Line-B.../dp/B001XRZRYI

T-9 works pretty good. Add some heat with a hairdryer also.

Standard Shimano STI "maintenance" is WD 40 flush then lube with new cables and housing.

​​​​​​https://www.google.com/search?sca_es...&dpr=1.1&aic=0

All the above should get it working for a while. You will probably need to repeat periodically as once the cleaner/lube/solvent/penetrant/displacer evaporates, that cursed Shimano OEM grease will gradually re-solidify and re-gunk.

If I'm sending a bike out for sale or donation, I prefer to try to get all the old grease out, which requires removing the shifter from the bike, an ultrasonic cleaner, patience, and maybe a freezer (optional). Details for the "more thorough" method are at De-Gunking Balky Shifters - For the Long Haul

Thanks!
But I thought that WD40 is not that great for plastic, and aren't there some plastic bits in there?

While mineral spirits (the main component of WD40) can damage some plastics, the kinds of plastic you find in Shimano shifters is unlikely to be damaged by it or the amount used is small enough to not cause that much damage. It’s useful for flushing shifters and in years of using it, I’ve experienced no damage.

We have used 3-in-1 penetrating oil for degunking along with a small pic to work the cog lock

One more opinion/anecdote.....

On my wife's early-2000's Gary Fisher Tassajara, I went after the balky trigger shifters with a handheld steamer that I already had on hand:

https://www.bissell.com/en-us/produc...izer-4155.html

And WD40. I did about 3-4 cycles of steam/WD (with steam being the final application), then gave the whole thing (on the bike) 24-48 hours to dry out, after which I lubed the internals with Triflow. It's been over a year and so far, so good.

While I have zero doubt that my method falls short of the nuclear option -- the one invoking the freezer and repeated, protracted ultrasonic cleaner cycles -- from that other thread ... it's good enough for me (and my wife) and was pretty darned low effort.

I generally use wd40 and an old toothbrush followed by spritzing with water and compressed air...I'd not used the compressed air for electronic systems...wipe dry as possible with clean cloth or shop paper towel then air dry but less water than what I usually use.

It's fine, it has been used literally by everyone for years. Things like brake cleaner you need to be wary of with plastics.

Hence why I present it as "here is how to solve the problem once and for all" vs. "this is how far you are probably going to be inclined to go."

I would not be surprised if most people would be heading to their LBS or searching online for new shifters prior to going the "thorough cleaning" route. But I post it to inform people about what it usually takes to get a good long-term fix, and to combat online misinformation that claims "do this flushing once and you'll never have problems again!!"

Meanwhile, I collect the discarded shifters and clean them as I'm completing other repair tasks, and everyone's happy.

Make certain it's the STI and not the cable binding somewhere. I might pull the far end of the cable out of the housing till getting to the one that is under the bar tape. And then put a little tension on the cable as I shift up and down. And if that's no change, I'd remove the cable entirely and try to gauge how much resistance as I remove it through the STI. It's possible you might have a frayed cable in the shifter. Those usually show other issues long before being thought of as a gunked up STI.

I wouldn't flush a STI unless it's a last ditch effort to make it work easily.

Have you clamped anything around your bar that might be collapsing the cable slightly? I did that once.

I will double check, but I am pretty sure that the gunk is the problem. I had the exact same behavior in the exact same shifter one year ago, and it was fixed by flushing. That was done for me (quickly, and maybe not very thoroughly) by a mechanic at an aid station during a century ride ten months ago. As RCMoeur says, this may not be the ultimate solution, but if it works I am OK to do it every now and then. I don't have access to an ultrasonic cleaner anyway....

Update: floaded it with 1 step, works again.
Thank you to everyone who made suggestions!

Although in pulling it up, I ended putting a small rip in the 12-year old hood, so I just ordered a hood replacement. There is always something....