Underwater video recording errors, compression artifacts? overheating?

I'm struggling with a problem shooting video when snorkeling. Maybe one of
you can help.

I'm using a Canon GL/1 in an Epic housing. I'm getting excellent results
for 20-30 minutes and then I'm getting what look like compression artifacts.
I'm getting bands of time/space shifted data in the frames. And the longer
I shoot, the worse it gets. When it first starts, I get just occasional
artifacts. After a while, I'm getting only one good frame out of every 7 or
so frames.

I notice that the camera is quite warm by the end of a 90 minute swim. And
I suspect the compression artifacts are worse on hot days. (I was out
recently in Belize and the problem was worse on days when the air
temperature was about 95 F.)

I've tried cleaning the heads and I don't seem to have any problems using
the camera out of water.

Has anyone else seen this problem and found a solution?

Thanks a lot.

David Liebtag