Dave Richardson wrote:

I found a patch on my airplane that does not seem to want
to hold paint.

<snip>

What will get rid of the silicone or what ever it is and be sure
the paint will adhere?

Your local auto paint store will have all sorts of fun
chemicals used to remove silicone, tar, fingerprints, etc.
Go in and tell them what you have done, and what you think
you have.

Pat