How to test distributor condenser? What makes them go bad?

I had a problem with my mallory dual point last winter. After putting in a condenser, cleaning the points, new cap + rotor etc... I got it fixed. Last week the problem came back, so I put in new points. That helped but didn't fix the problem. I put in all new stainless screws and a new condenser and it's running good again. Both condensers were genuine mallory, the new one is a napa echlin. I still have both old ones, is there a way to tell if they are bad? What would make them go bad in a year? Not many miles on them? Thanks.

Now that I think about it, the first thing I tried last year was to change the condenser, and that didn't help. I just wish I knew what exactly I'm doing right to keep fixing this probem, and maybe prevent it from happening every 6 months.