The pencil zinc on the Universal M-25XP is the bolt you will find on the bottom of the heat exchanger (located on the back of the engine above the transmission). To check it; first be sure your engine seacock is closed, then unscrew it. There will be a bit of water that comes out but not enough to worry about. You can get replacement zincs at any marine store however you will probably need to cut the end off with a hacksaw to get it to fit. I haven't been able to find one that fits without cutting yet. I would recommend pulling port side end off the heat exchanger, if it hasn't been done in awhile, to check for chunks of old zinc that fall off and can block the water flow. Hope that helps, Roy
