Also, I'd LOVE to see what you are working on!!!!!I like your sculpt!
When I had a issue with some silicone not curing well, it was actually the bolts holding the mold together, the mold was fine. But if I had touched the bold and then handled the mold, I could have issues. Problems can come from unexpected things.
For what you are trying to make, it seems like Ecoflex would be a great choice and you wouldn't need Slacker which seems to be where you are getting problems. I have limited experience, but both Dragon Skin and Ecoflex are fantastic and have given me great results. I am about to start a new project that will have a thin layer of Dragon Skin 10 on the outside, then backed with Ecoflex 00-20 or 00-30.
The Stan Winston online school has a recent 3 video series called Silicone Mask Making where the people from Immortal Mask go through their process of molding and casting silicone masks. Every tip they give is useful and I wish the videos had been available before I wasted tons of money trying to make molds. I think it is well worth joining and watching the videos if you plan to make more molds in the future. Even if you don't use their exact process, just knowing how they deal with silicone and such is useful.