While I've never done a P89DC, I have fooled with the P-85 a bit. However, if you can get a copy of the "Gun Digest Book of Firearms Assembly/Disassembly" Part I Automatic Pistols, it'll have a very detailed photo instruction on the P-85. That should pretty much help you replace the firing pin. If you need any parts, I have a bunch for the P-85 & P-89 too.