Starter, start-her sometimes

[A79alfa@domain.elided]

 My 79 spider has developed a little problem recently. 
The starter sometimes does not work, I ran a wire and a switch under the dash
so as not to fuel the theory that Alfa's are unreliable to onlookers.
Do you think it's the starter or is there a solenoid or something else?
It has only done it maybe ten out of a hundred starts. 
But I would like to fix it ASAP.
Any help is greatly appreciated. Thanks.
Mike Ferrone
79 spider
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