Anyone have advice on rebuilding a distributor?

When setting timing the mark will jump to a location about 20 degrees advanced every fourth flash. I suspect the distributor. How can I fix or rebuild it? It's a 3.0 95 Toyota 4runner. I have the appropriate cables jumped as per manual in order to byp ecu controlled advance. Oh and I already replaced cap and rotor. I wanna know what people do when rebuilding the housing if it's just a matter of replacing the gear down there or what.... Thanks!