Wheels really are not "parts" per se, as they are very interchangeable for specific applications. I have several wheel sets, and tend to swap them out based on what cog or whether I want tubulars or clinchers (across 3 bikes). Half the time my wheels don't even match (like if I am running a brake and don't want a nonmachined surface up front.... or whatever).

Where exactly is the crack on your seat tube? Is it above the weld with the top tube?