There is no bulb that will stand up to water when hot, so you're going to have to find and fix the leak. On a dry day, spray down the front of your scoot with a garden hose and see where it's getting in from, then you will have a handle on how to seal it.
The extra bulbs are the non-US turn signals, they are not separated widely enough for US regulations so kymco add the extra ones on stalks for the NA market. A common tweak is to wire them up as running lights