Delta B767-17-19 Feb intermittent transponder failures

[j636]

All the same aircraft:
Incident: Delta B763 over Atlantic on Feb 17th 2012, unreliable transponder (http://avherald.com/h?article=44b36c0c&opt=1)
Incident: Delta B763 near Prestwick on Feb 18th 2012, unreliable transponder (http://avherald.com/h?article=44b36cc7&opt=1)
Incident: Delta B763 over Canada on Feb 18th 2012, unreliable transponder (http://avherald.com/h?article=44b36e48&opt=1)
Incident: Delta B763 at Dublin on Feb 19th 2012, unreliable transponder (http://avherald.com/h?article=44b36f9d&opt=1)

Can sombody explain how this aircraft was allowed to proform these flights and if it was repaired why did it contuine to fail.

[aviatorhi]

Because there's some gremlins and mx is tracking them down.