Try looking at the possible cracked areas with a magnifying glass and strong light. Look at the crack obliquely (from an angle) and try shining the light through it back towards yourself. You might be able to see if it penetrates the thickness of the housing wall.
I would bet that String's marks are just mold marks, but of course observe them closely.
Are these cracks in areas of the hosing which might get bumped repeatedly? Are they in areas where the latching mechanism is putting a strain on the housing material?
Putting a drop of with cyanoacrylic glue (crazy glue) or an acrylic solventcementmight seal and stop the crack. Though Ikelite should be your first contact before doing this.