Radio Shack sell an IR detector strip that costs a few dollars. This will make it easy to see if IR devices are working or not, you can also see low battery conditions as well!
Another way to do the same thing is to use a ccd camera, most of them are sensitive in the IR band.
"If" you are burning out the LED's then it could indicate a hardware problem on your unit. This is highly unlikely but is possible. It's much more likely that the cable box adjusted it's software, or the led moved a bit, or some new form of IR interference was introduced, ... If you have an O-scope you could measure the signals on the IR emitter and see the signal being sent. You could then compare those to the signal send from the cable boxes remote. You would need to build a simple IR detector. There are expensive IR decoder/tester boxes as well.
Also search the archives for other reports on your particular cable box.