Had a very similar problem on a VVRC 20 cc.(very similar to a DLE) The needles kept requiring attention and I noted oil on the crankcase. It turned out the four bolts holding the head to the case were loose ever so slightly causing an air leak, Tightened them, problem solved.
As you hit hard enough to break a fin this may be possible, It may also be possible the ignition is damaged? Eliminate the Opti-kill to see if that is part of the problem they sometimes act up? Had an RcExel mod. that worked for seven mins. on each flight and started missing and would quit, changed it and problem solved.
Good luck!