Source: Aaron Gleeman, NBC Sports 
At this point the Nationals have been linked to basically every free agent reliever who throws the ball left-handed and the latest is Oliver Perez, with Adam Kilgore of the Washington Post reporting that they “have significant interest.”
Since shifting to the bullpen for the Mariners in 2012 Perez has thrown 83 innings with a 3.16 ERA and 98 strikeouts.
But here’s the funny thing: Perez pitched for the Nationals at Double-A in 2011, starting 15 games with a 3.09 ERA and 58/27 K/BB ratio in 76 innings, but they let him go.
And then the Mariners turned him into a valuable reliever.