That's a Mobella lock ass'y. You can look it up on Southco/ Mobellas website. I found a picture of it on yachtworld dot com under a 1992 538 Montego. It came up on the first boat (Southaven MI), scroll through the pics and you'll find it. I also found an older (1990) 35 Montego with door pictures (Eastlake, OH) and it shows a different style of lock assy. Look them over and see which one you might need.