Yep, that's what I thought it would be, as mine was exactly the same as yours.
It's down to the antifreeze not being changed and the system not being flushed in a long time which causes corrosion build up.
As 1984mini25 says, make sure you fit a good quality bypass hose and ensure you clean out all of the waterways before you build it back up, otherwise you'll have to take it all back off again.