Hi @zillah
I don't think there are any perfect silicone cleanup solutions out there. Results will vary with different products as you have already discovered.
Some times leaving the chemicals there longer will help or apply in stages as you wipe silicon layers off. Fastest way is to physically remove as much as possible then chemicals can get the last traces faster.
After reading the descriptions of the products you did a great job on researching by the way.
The common instruction is to cut or scrap a lot of the silicon bead first to make the cleaner more effective on the remaining silicon bits that stays attached.
So how do I remove gutter silicon might be the way forward here to guide you.
Physical removal is the quickest and less messy where possible to get at the silicon. In a gutter this isn't easy access and cramped spaces for your hands. In this case use a longer tool to get in there where your hands wont go.
Tips on gutter repairs I think the best way is to use two A frame ladders with a aluminium plank in between will get you up high enough to see your work and safely use tools (single story) to be in a safe comfortable work position. An industrial plank saves a lot of ladders climbing and moving if you have the whole gutter to restore. Avoid ladders with rounded rungs for longer working sessions they hurt to stand on after a while and may make us more distracted up a ladder. Do wear flexible cut proof gloves as those gutters full of sharp metal edges. I explain this in detail as to help other readers too. Ladders leaning on the gutters will flex them in making it extra tight space to work in best to use a ladder with facia stand off and clamping attachment to stop things going sideways fast.
I will cut the silicon with a thin bladed utility knife. down the longest edge where possible then peal it off in long strips. I also cut into gaps both sides.
This will leave bits of silicon behind. I like using a metal dish washing sourer as it doesn't clog up too fast and it doesn't hurt powder coated metal gutters like a wire brush will. If I want an extra silicone free gutter, I will dip the sourer in turps or sometimes petrol. (Petrol has being quite good at jellifying the silicon in the past.) Any remaining silicon in the corners or joins I use a small flat bladed screwdriver and run it along the edge or into gaps as a scraper. This will leave a cleaner residue that must be now cleaned before re siliconing.
Now if you wanting to reapply fresh silicone wash down the area you just cleaned with methylated spirits on a clean rag to help remove your dissolving chemicals. The methylated residual will evaporate quickly by itself.
If you are in a comfortable work position the extra time silicon removal takes is much less of a chore
