Since Olympus wants to charge $148 for the diffuser, consider buying a new housing for $180 (that's what they sell for on eBay). I know this diffuser is more complex than most, since it guides the light from the strobe to a diffuser plate in the front of the camera, and snaps to the body on both ends. It would be time consuming to make a replacement, but could be done.
Or consider going to external strobe exclusively. There are several ways to do this. Use the HeinrichsWeikamp converter and an inexpensive Nikonos compatible strobe, or the Olympus strobe housing and FL-36 strobe. I don't know what solution Ryan suggested for you, but I would bet there are some PT-023 housings with broken port clamps around to cannibalize. I heard his shop is no longer supplying Olympus housings because the latest lens ports are attached with flimsy clamps that don't hold the port on in rough seas.
I use the PT-027 housing, which has the similar clamps, but for a smaller lens port. I always worry they will fail, so I am very gentle with the housing when diving. Despite this, I have found the clamps moved off the lock position during a dive, but I was able to move them back and did not have a leak. Scary.
This design is terrible. I am considering taping the port to the housing or drilling the recesses in which the lock pin sits a little deeper to prevent a separation. I wonder if anyone else has seen this problem with the port clamps? I note that for the Olympus E-series housings, it appears that Olympus uses a very different port attachment, a screw-on port like the Ikelite port system for Olympus point and shoot cams.
