Re: what makes timer bases fail?
There is no way to test for it, but very often the power pack will cause a timer base to fail. Your 70hp timer bases uses logic chips to change the start timing - QuikStart - and they are very critical to correct voltage and any voltage spikes. Replace the pack and timer base together if there is a history of multiple failures. Also check the coil grounds, wires, and for any cracks in the insulation as a marginal coil can affect a power pack which in turn can affect a timer base.
Do not use plugs besides the factory recommended "Q" series which use a suppressor internally, not a resistor like other brands.