FamilySearch is gradually adding features to their Beta site at http://fsbeta.familysearch.org. A user can search for records on the FamilySearch Record Search site using the simple search fields on the Beta home page, shown below:
Notice the "Show Advanced" link below the "Death Year" field. If you click on the "Show Advanced" link, you see many more search fields to help you with your search:
* Death Place (with an Exact check box)
* Residence Place (with an Exact check box)
* Mother last name (with an Exact check box)
* Spouse last name (with an Exact check box)
There were 1,880 matches for my search terms, including many that were obviously not a Benjamin Seaver born in 1791. There were no matches for my Benjamin Seaver, born 1791 and died 1825 (which I didn't add to the search field). Presumably, that means that FamilySearch has no historical records for this particular Benjamin Seaver.
The match is a mention of Benjamin Seaver in the Revolutionary War Pension application for Nathaniel Houghton. The link to the record is to www.Footnote.com. The reference to Benjamin Seaver in that record is for the father of Benjamin Seaver (1791-1825), also named Benjamin Seaver, who did serve in the War.
While this match in the 1865 Massachusetts State Census is for a Benjamin Seaver, it is not the one born in 1791. It is for his grandson, born in 1854. The birth year, or age, for this person apparently was not indexed for the 1865 Massachusetts State Census on the FamilySearch Record Search site.