If you were to log in, you'd be able to get more information on your fellow community member.
I prefer safety wire to cotter pins, even with slotted nuts, and then using a bit of structural epoxy to hold the wire. Frequent inspections are also important. Now that you've identified this weak point, you should inspect the location frequently. And given the institutional engineering philosophy at Diamond that allowed that poor design decision to be made, have you checked your airplane for other instances of bolt ganging that create critical single point failures?