There are two ways to check, if you zoom at tele end with the camera in there should be no to little distance between the lens and the glass port, if it looks like there is a small gap measure the port.
I measured the original port that came with it and it is 1" 5/8" or 412mm, if you have this one it needs replacing. Consider however that there is no vignette with the wet mate, the problem only occurs with the wet wide lenses. In terms of optical quality the shorter port should also be better in terms of chromatic aberrations.
The new port is 1" 1/2 or 380mm from the housing to the end of the M67 thread
If yours has the longer port you need to ask your dealer to send you the new replacement port