These magnetos reverse polarity through the points with each change of the magnetic polarity from North to South, etc. as it rotates. Any transfer of material gets reversed with each subsequent change. Distributors always transfer material in the same direction, and occurs not only at the points, but also at the rotor tip and cap terminals.

In a distributor with breaker points, when the balance between the capacitance (in the condenser) and the inductance (in the coil) are perfect, there will be no transfer of material in the points. If you ever see this happen, do NOT touch it!

  

Try to find any distributer parts today that are of the quality you could find 25 years ago. Magneto parts available ate this point are probably that old and when they're gone, they're gone. 

I beg to differ. I would take a Distributor any day over a Mag.  I rebuild Mags, but I'm slowly moving away from rebuilding them due to the lack of good quality service parts. Quality parts for Mags have diminished. The cost to rebuild a Mag now a days gets pretty expensive depending on age, mfr. model, series & condition.  With a Distributor, you can at least still get decent quality parts for them (non Chinese) as well as adding an optional electronic ignition. Like anything else mechanical, Distributors need to be attended to and inspected once in a while as well. Keeping a good EP Moly grease in the drive cavity is a plus to keep gear mesh wear to a minimum, as well as checking Distributor main shaft runout for peak performance. In most cases, a properly rebuilt Distributor top to bottom will give many years of service with normal intermediate inspections. I've changed over many a frustrated customer from a Mag to one of my Mag to Distributor conversion kits, and they never looked back whether points or E.I.

Steve@B&B