Tyvek tape is the bomb! It has a permanent waterproof adhesive meant for weather proof construction applications---it will not turn gummy, dry out and and fall off like duct tape. It will definitely stick to silnylon. I use it to patch my water bladders, has held up for 2+ years at this point, still 100% water proof and bonded. No seam sealer. Just clean the area and tape it. You can use it to patch rain gear and it won't fall off in the wash. Patch your tarp, bivy, sleeping bag, etc.
The only problems are that it costs more than $20 for a roll and is impossible to find at a normal hardware store, try online. One roll will likely last you a lifetime.