I am fairly sure it has been attempted to "fix" leaking hydraulic cylinders many times and without very expensive equipment it just is not possible. I remember a few years ago there was a guy who said he had done a successful DIY to come back two weeks later and ask for the address of the "guy" who refurbishes leaking top cylinders. My guess is, you won't have success with simply putting some silicone there and I'm also guessing you might do more damage than good.
Sending them in to one of the recommended vendors might be your best bet.