I finally examined my housing. It looks as though Olympus has molded guide holes into the housing to accept self tapping screws. If the screw was over torqued, out of spec (wrong size); if the hot-shoe plate was out of spec (hole slightly offset); or if the hole wasn't molded properly, one might expect this result.
Again, are you using the hot-shoe to hold anything? If you are using the hot-shoe was the item mounted there maybe a little big, did it have to be forced? Or was the mounted item torqued or bumped, maybe even unnoticed? These are other ways to crack the housing.
It is possible to see slight distortions in clear molded plastics. It's also possible to see minor distortion and crazing where screws have been applied. Viewed with polarized light there would ball sorts of patterns visible in the material.
The structural integrity of the housing probably isn't too badly compromised. The crack extends through an external rib not into the housing itself.
If Olympus won't respond or repair the housing, here are some possible DIY solutions:
Slightly backing out the screw(s) (1/4 turn or so) might relieve some of the stress, especially if you are mounting anything in the hot-shoe.
Infiltrating the crack with a polycarbonate solvent/cement might glue things back together.
Infiltrating it with a product like crazy glue might also help, but wouldn't be quite as strong.
Just sealing the crack with silicone (RTV) wouldn't be strong, but would seal the area.
Leaving it alone, especially if you aren't using the hotshoe would probably be ok too.