By "plunger," I mean where you actually press the lock and push it in to lock it, and a center pin comes out the back and goes into a hole in the frame of the other side of the sliding door. To unlock, you have to use the key and the "plunger" pops back out. That's what is on our 460 EC, I just got a new one for it (it's an Abloy lock) from an outfit in San Francisco. About $40 and $5-10 per extra key. It was a PITA to install but it's on. I'll get the info for you....but I think it was bayarealocks.com -- they seem to be able to solve just about anything for marine use.