According to Joel Sherman of the New York Post:
I hear the Mets keep trying to find a place to deal Ramon Castro. They have two reasons: 1) Mainly they want to get rid of his $2.5 million 2009 contract, allowing them a little more available cash to address a righty bat or lefty reliever they crave. 2) They believe that for near minimum wage Robinson Cancel can be just as good a backup to Brian Schneider as Castro. I heard the Brewers had some interest, but have mostly backed off of Castro now.
Castro, 33 in March, hit .245/.312/.441 last year in 157 plate appearances (he spent time on the DL for a strained quad and hamstring). He's shown good power in limited duty. He had two issues in '08: his pain tolerance was questioned by Jerry Manuel, and he arrived late to a June game. He's set to earn $2.5MM in '09 before he reaches free agency.
It seems unlikely the Marlins would reacquire Castro; his final year with them in '04 was marked by rape charges that eventually led to a no-contest plea for misdemeanor assault. Castro's salary would be the more obvious obstacle for them.