Had the same problem on my EL wagon when I had it. Turned out to be as the other guys said it was the tailgate mechanism. Didnt have any CRC so found a new use for Start ya bastard . Gave it a good soaking and fixed the problem.

I had to put this on at least one thread on the internet. On our ef wagon we disconnected each actuator one at a time and it turned out to be the tailgate. The entire locking mechanism was siezed and all it took was some spray lube and a s**t load of jiggling the linkages. Fixed it no worries.