That appears to be non-serviceable.
Note that on the end of the case with the electrical connections, the metal part of the body is bent inwards to hold the piece with the electrical connections in-place. You could use a screwdriver to bend that lip back outwards (making a really ugly mess of it), pull it apart and replace bits and pieces, put it back together and use a punch to bend the lip back into place (no, really, I've never done anything like that in my life
), but the probability of success and reliability of the result aren't worth it. Besides, the solenoid is sealed to avoid having sparks ignite any gas vapors in your bilge, and doing this would break the seal. Can you say bad day at the lake? I knew you could...
I think it's time to get a new one. It should be a readily available part.