Its probably been circling around in the ocean vortex for a year and a change in conditions has fired this piece out. I think there are bits and pieces from world war 2 still floating around in these vortex that wash up from time to time

Yes, you're correct it's incredible how long things can stay in ocean currents but not surprising given the size of our oceans and complexities of weather and tidal systems.

Things from ancient shipwrecks wash up from time to time, the Tjepitir blocks from the 1800s are still being found!

On our shores we often see Lego blocks washing up from a container lost in the late 80s and it is believed that most of them are still floating around.