Recently while taking apart my boat I noticed that I have water sloshing around in one of my crossbars. Removing the end caps doesn't do anything. Do I need to drill a hole to drain and then patch? If so, patch w/what - marine silicone?

I also noticed what appears to be some kind of yellowish foam in my upper boom only about a 6 inch section. I never noticed or felt it whenever I raised the sail. It is in the track of the boom. Can or should I remove it? I have a float ball so I can't imagine what it's purpose is?