Oh, sad to hear the death of your A70. Oh man , 3 year old O ring ? Why dun you get a replacement from Canon ? It cost S$20-S$25 over at Singapore. Not willing to pay that kind of $$ for an O ring, I search for an alternative . Althought My A95 housing is less than 3 mths old, I took no chance. Its always good to travel with spare O rings.
Search and found an O ring supplier. Brought my Original Canon O ring to him, he measure the length and diameter, and gave me an O ring with exact dimensions, and said that the O ring material is the same as my canon one. i bought 5 in total, for my A95, and friends' A70 , A75 , A80 at a fraction of the cost of an Canon one.Cheap
After I got home, did 3 tests to confirm that it will work with my canon housing.
Test 1 : Apply the silicone to the o ring to see if it will cause the O ring to expand.To see If the o ring material is not suitable for the silicone.
Result after 72 hrs: O ring did not expand, safe to use the silicon gel on this O ring
Test 2 : Put it in my housing, and soak at home in 1m of water for 3 hrs. If its not fitting, at 1M, it will leak.
Result : No leakage detected
Test 3 : Brought it down for diving to 20m, empty housing.
Result : No Leakage detected and camera was loaded into housing for subsequent dives.
Friends have not dived with the new o ring yet. But should not be a problem as they compared and find it to be same size as the Canon ones