I have had quite a few people bring Canon Compact Housings to me for help over the last couple of years, as they have had small leaks for no apparent reason. These housings have mostly been the G7, G9, G10, A610, A620, A630, A640, A710, A720.
What I have found on close inspection is that there are 3 or 4 mould release lines (no. of lines depending on the model) in the main ‘o’ ring groove on the door. These ‘lines’ run across the groove and very obviously would stop the ‘o’ ring seating in the groove correctly.
It seems that most people have leaks in the shallows with their Canon housings. Either on descending or after a deeper dive with no problem, a leak is evident as they ascend into the last 10 meters. This is typical of an ‘o’ ring that has not seated correctly, so that’s why I started looking closer.
I had one desperate photographer who wanted me to try anything to have their housing fixed. So I promised to find the leak source. It was a Canon G9 housing, I could see the water entering the housing as a very small drip that ran down the ‘O’ Ring until it pooled at the bottom.
I decided to sand the Mould Release line, as this was exactly where the drip eminated from. I used a piece of very fine wet&dry;sand paper (600 grit), I wrapped a small piece around a small aluminium ruler (about 2mm thick), then gently sanded the mould release line, until it was level with the bottom of the groove.
I actually did the sanding a step at a time and inspected the progress with a magnifying glass (Actually I used a ReefNet SubSee Magnifier, as it was stronger than a magnifying glass) and progressed until the mould release line was finally non-existent and the ‘O’ Ring groove had a flat bottom, rather than a step at the Mould Release line. It was quite easy to see the problem with a magnifying glass before sanding, and that it was smooth after the sanding. I also sanded the other 3 mould release lines in this particular housing, as they also were raised more than they should be.
I was so confident that I had fixed the problem, I took the housing with its camera on a dive immediately after fixing it, and it was dry as a bone…. which it hadn’t been for quite a few prior dives. It has since proved to be perfectly sealed and hasn’t leaked since.
Check-out your own housing if it has these mould release lines, I’d get it fixed pretty soon.
I have now fixed more Canon Housings and all have been successful. I have also just fixed a G11 housing that leaked on its first dive, it had exactly the same problem. It also explains to me why some housings leak and some don’t. This mould release line is more evident in some housings than others.
BTW, I also manufacture an electronic Leak Detector for the Canon G7, G9, G10 & now G11 housings - see the web link below.
Photos & Sketch following so you can see how to do this work yourself.

Here’s a couple of pics of the “Mould Release Line” - First Pic shows one end of the door, with Two Lines marked with arrows. The other end of the door also has two lines in the same positions.
I have found that the one shown here on the Left is the one that causes most leaks, but its easy to fix all 4 while you have the sand paper out !

Second Pic shows a close-up of the Left Hand “Mould Release Line”. When it is sanded this line is no longer visible, and you can’t feel it when a toothpick is run along the groove. I have now heard from around 15 people that I did this modification too their housings, and all have done plenty of dives with absolutely NO LEAKS.
P.S. Please don’t ask me if I can fix your housing “Mould Release Lines”, it is so very easy to do yourself.

Following is a sketch to show you the details on how to do the work:

Thanks for the technique, I hope it can use with other housing brand.

paulgladi - 26 March 2010 03:28 PM

Thanks for the technique, I hope it can use with other housing brand.

Hi Paul, so far I have only seen the large ‘Mould release line’ running through the ‘o’ ring groove on Canon housings.
But I have also seen them on Fantasea torches, particularly the Fantasea 360 LED and Fantasea 44 LED models that a lot of underwater photographers use for focusing lights.
This one is even easier to fix as it is very easy to see the mould line (it runs down both side of the torch body including the thread for screwing the head-on). Just sand out the line where it runs through the ‘o’ ring groove (As per my instructions above for the Canon Housings).
I had two Fantasea 360 LED lights leak on me (Both 1st dives in 10-15 metres deep), I managed to save one from drowning and do the modification, it has now done a couple of hundred or more dives and has never leaked again. Fantasea recalled the torches a little later - due to leaking problems.
I then ordered a new 44 LED (which wouldn’t have the same problem… apparently) and guess what, it also had the ‘Mould release lines’, I didn’t dive with-it, but sanded the ‘mould release lines’ and it has now served me well on 50-100 dives without a leak. These are very good torches only let-down by final finishing!!!
Guys it’s all about QUALITY CONTROL .....