Spare Oring for the following Panasonic waterproof housings:

Panasonic DMW-MCTZ20
Panasonic DMW-MCTZ10
Panasonic DMW-MCTZ7
Panasonic DMW-MCTZ5
Panasonic DMW-MCTZ3

Most manufacturers advise replacing the main o-ring once a year. It's also wise to take along a spare oring on your diving holiday!