This would appear to imply that the hydraulic system got too hot or there was a leak in the system to begin with. Lots of questions come to mind.
1. Must me missing a tile somewhere?
2. Loss of control of left wing due to hydraulic leak.
3. Wonder how the hydraulic fluid thermally decomposes?
4. Is there enough air for combustion?
5. Burning jet of hydraulic fluid causes other problems?
I was looking into risk earlier. Risk-wise NASA counted on a loss of 1 in 50 shuttle flights when the program was originally conceived. The risk has certainly gone down significantly in the wake of Challenger, but we were probably overdue. I have found a more recent briefing which indicates the loss rate is now calculated to be 1 in 250 as of 2002 which is an amazing number as far as space launch is concerned. I think we are well over 150 flights now. Their aim at the time of the briefing was 1 in 500 by 2012. Here's the link.
http://www.hq.nasa.gov/office/codeq/safetydir/Wednesday/stamatelatos.pdf
It truly is rocket science.
I'd discount the pre-existing leak idea. Hydraulic temp increase is, however, apparent. Now, for the questions as best as I can hazard an answer...
1. Must me missing a tile somewhere?
I'd say more than one and concentrated around the left gear door, probably including said door.
2. Loss of control of left wing due to hydraulic leak.
Possible. I don't know about any manual backup systems, or where the control surfaces default to when hydraulic pressure is lost.
3. Wonder how the hydraulic fluid thermally decomposes?
Unknown.
4. Is there enough air for combustion?
No, unless an oxygen tank popped a leak.
5. Burning jet of hydraulic fluid causes other problems?
If there's burning fluid, definitely.