I have a 41mm Macro Port for Nauticam Housings
There are no marks on the port and the glass is in perfect condition.
This Port is used for Canon EF-s 60 2.8 Macro
However it also works with the Canon 100L Macro with 70mm extension (perfect for travel if you have the 16-35 Dome and 60 extension)
Includes the back cover.
New price is $400
Happy to take US$250 plus postage and paypal fees, postage from Australia to USA will be about $30