This cut down the number of times that the dials would fail - but on ITT's first dials, they used some pins that would slide into sockets to connect the dial electronics to the button PC board. They used a cheap material for the pins and sockets, so oxidation would develop pretty quickly. The fix was to slide the board with the connector up and down a little on the pins, to clean off the oxidation. This would fix it for a little while, but a new dial was the real fix. The rubber button type keys are not self cleaning, but because of the size of the area that makes contact, there are relatively few contact problems except in really dirty environments.
Most telephones use conductive pads that are conductive thru and thru.
Be careful with the traces on the circuit board that are not shiny metal, but a raised carbon track. It's easy to take off too much of the conductive material, and the trace will be dead. It's easy to test the conductivity of a rubber pad or PC board trace. On most pads, you will see 100 to 200 ohms. If you test a bad pad, it will often read 500 to 10,000 ohms or more.