Can a pellet gun be rebuilt?

Yes, But first determine if it's worth it. Some inexpensive pellet guns are not worth rebuilding. Marksman makes a line of inexpensive air guns and rifles that are not considered very high in quality and may cost more to rebuild than they are worth. However Beeman (Who Owns Marksman) makes very good air guns and rifles, and would be worth the effort to rebuild one.

There are several air gun shops around the country that make a living repairing older air guns. You can do a search on the web for "Air gun repair" and locate one that works on your model. Unless you are very handy with tools I would recommend one of there shops, rather than tackle the job yourself. Crosman offers a link on their homepage to independent shops that repair Crosman, Benjamin and Sheridan air guns. All these brands are owned by Crosman.

So yes most air guns can be rebuilt.