The Collaborative International Dictionary of English v.0.48:

Sealer \Seal"er\, n.
   One who seals; especially, an officer whose duty it is to
   seal writs or instruments, to stamp weights and measures, or
   the like.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sealer \Sealer\, n.
   A mariner or a vessel engaged in the business of capturing
   seals.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sealer
    n 1: a kind of sealing material that is used to form a hard
         coating on a porous surface (as a coat of paint or varnish
         used to size a surface) [syn: sealant, sealer]
    2: an official who affixes a seal to a document