system
Given the following post, respond as if you're commenting on Reddit:
human
What components on the Opportunity rover have failed so far and how has that affected it's usefulness?

As a follow-up question, assuming the solar panels continue to stay clean and absorb enough sunlight, which component is most likely to be the killing blow upon failure?
gpt
On Sol 2 they realized a heater on the shoulder joint of its arm was stuck in the on position.  They've had to play with the power system and the joint to keep it from draining the battery at night, but it has become damaged from the temperature swings.  Now they no longer stow the arm unless they're moving, and immediately extend it out again after.

In 2015 one of its 7 flash memory ships started failing resulting in system resets.  They updated the rover's memory systems to ignore the failing chip, and its working fine.

Aside from those the periodic dust build up and wind/dust devil cleaning of its solar panels appear to be the only other *issue* that Opportunity has had.

*EDIT*
Wheel failure will probably spell the end of the mission one day.  If the rover suddenly can no longer move and its solar panels aren't in a favorable allignment with the sun its power will eventually drop, as it did for its sister rover *Spirit*, to the point of complete power failure.  After that they probably won't be able to get it to power back up and the mission will be over.