Maynard & Allison -
The housings have door-gaskets, the o-rings are on the control buttons. My Oly PT-015 housing for the C-5050 has two door-gaskets. Allison is right - one of the gaskets on the Oly housing has a tendancy to slip off and get caught in the door when it's being closed. Maynard is also correct, with proper maintenance and care gaskets will protect your investment regardless of make or design.
Many Ike housings have only one gasket - some have two, one on the door and one on the lens port. Some of the Oly housing have one gasket, others have two.
There are two types of gaskets, "free" and "compression." "Free" gaskets need to be lubed because they seal by moving under pressure. Lubing a gasket is an invitation to hairs, sand, etc. The "compression" gaskets do not require lubrication as they do not move, but seal under pressure. This lack of lubrication means compression gaskets aren't as prone to attract hair, sand, etc. In transparent housings, you can see when a compression gasket is sealed. It's always a good idea to examine the seal under a bright light before getting the housing wet. The Ikelite housing gaskets are of the compression type. The Oly PT-015 has one of each type - double protection!
All o-rings & gaskets have to be carefully maintained and no matter if it's an Oly or an Ike housing, they will leak if you aren't very, very careful. Someone said, "it isn't a matter of if your housing will flood, but when."
[Knocking on wood...I've done hundreds of dives with Oly housings and not had any floods. I now have an Ikelite housing.]
