The 23-year old Australian attacker netted the opening goal in just the third minute as Frankfurt took an early lead at the Fritz-Walter-Stadion but Kaiserslautern levelled in stunning fashion in the 23rd minute thanks to Florian Dick's volley.
Mohamadou Idrissou had the home side ahead eight minutes before the break when he converted from the penalty spot before Andrew Wooten equalized for FSV a minute later.
But Kaiserslautern again rallied courtesy of Markus Karl as they went fourth on Germany's tier two table, three points within third-placed Paderborn, while FSV dropped to 15th, just three points above the bottom three.
Leckie's goal was his ninth league tally of the season which takes his total to 11 in all competitions in 2013/14.
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