Brass is a natural material, it will oxidize and form a patina or tarnish when it exposed to air or moisture. The outlook of the ring & the edge of the brass might have visible scratches due to the production process. It will not affect the clarity or impression of the seal. You can bring its luster back with sandpaper or in an eco-friendly way, such as lemon juice.
Each seal is individually engraved & mounted on the ring, variations may be presents that add to the uniqueness of each ring. The image engraved might slightly off center & might see glue marks around the brass.
Suggest removing your ring before contacting water or using chemicals.