Is my car distroying distributors?

[97ka-t]

Long story short- my 1998 240SX needed a new distributor. I bought one (used), replaced the old, and same problem. Bought another one (used), replaced the 2nd one, and still same problem. Prior to putting them in, I checked it out, and all parts looked to be in good condition, I even had a guarantee on the last distributor. Timing has been adjusted all over the place from advanced to retarded to advanced again with no difference, plugs were replaced, wires were replaced, O2 sensor was replaced, and the only code the ECU is throwing is 21 (Primary Ignition) which is indicative of distributor issues.. Could there be something that is causing them to fry, or is it simply the fact that they're used? Should I just suck it up and fork over $275 for a new one? What would you guys recommend?