Help: Intermittent starting problem

[SCforme]

My 84 Carrera has always started immediately with the first turn of the key. Over the past few weeks, it can take three or four tries before it starts when it hasn't been run for a few days. Once it does start, turn it off and it re-fires immediately. Replaced both crank position sensors a couple of years ago with OEM parts so don't think that's the problem. Any ideas of what this could be? As always, thanks for the help.