My front turn signal bulb went out; I can't read the number to replace.  One local store says it's part 1157, another says 7528.  What bulb replacement should I use?

Also the socket piece has rust on the metal contacts.  Does the plastic socket piece come all the way out of the rubber boot or is it hard wired in?  Just unsure how to gain access to remove the rust.

My lens cover looks fine so unsure how the water is getting inside to rust and how I can prevent water from getting inside the lens covering.  Appreciate any suggestions...thanks