Did some research for fixing silicone objects recently and found the following information:

Bonding Silicone Rubber
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Silicone Rubber
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Silicone is a high performance elastomeric material. It has a wide variety of uses and is often found used as seals or gaskets due to its flexibility and ability to be compressed between two surfaces. Other uses include flexible medical devices and tubing, prosthetics, surgical implants and special effects in the film industry. Thanks to its high temperature resistance, it is becoming popular in the kitchen for items such as non-stick bakeware and molds…. Maybe the “non-stick” is a bit of a clue when it comes to trying to bond silicone material.
In its solid, cured state it is normally very flexible, stretchy and... hard to bond!

Surface Preparation
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There isn’t much you can do to improve the surface of the silicone, it is always going to have plasticisers migrating to the surface to add to bonding woes! A solvent wipe with isopropanol will prepare the surface for bonding and remove any processing lubricants present and give a consistent bonding surface. Acetone can be a bit aggressive and other cleaners such as meths or white spirit can leave a residue. Always make sure all solvent is fully evaporated before bonding.

Adhesive Selection
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This is quite a short section as there are not many industrial adhesives options available to a poor soul looking to bond silicone! Silicone-based adhesives tend to work well on silicone but if you are looking for a fast cure and to get away from isocyanate chemicals then options are limited. A polyolefin primer such as Permabond POP can be used to prime the surface of the silicone and then parts can be bonded with a cyanoacrylate. Permabond 2050 is a favourite for bonding silicone as it is flexible and it doesn’t affect the “feel” of the silicone – it can be very hard to detect the bonded joint as it remains soft like the parent material – this is great for seals and o-rings as you don’t end up with a “crunchy” hard bit.

I selected this:

Smooth-On Sil-Poxy Silicone Adhesive - 3 Ounce Tube

Price:
$28.71 + $7.49 shipping
Ships from and sold by Smooth-On, Inc..

Description:
One-component adhesive made specifically for bonding RTV silicone rubber to silicone rubber and other substrates including some plastics (urethane), plasters/ceramics, fabrics, etc.
Works with tin- or platinum-cure silicones and provides a strong, flexible bond between silicone parts with high elongation
Can be used for repairing torn silicone rubber molds, bonding silicone for prosthetics and animatronics, etc.
12 minute cure time, Translucent