[Crifasinator]

Hi all,
I am new to boating and to posted up an intro in the general forum. My last trip out the rotor in the distributor broke the metal arm that contacts the cap. It seems strange the cap and rotor had been replaced by the PO and looked almost new. I noticed the cap doesn't mate to the distributor well and rocks on top a bit. It had left us stranded so I bought two new rotors and a new cap. is there anything I should look for that would've caused it or was this just a rare problem? I need to put the new cap on still hopefully it will fit more snug. I'll report back. Thanks
Anthony