Start Problem 98 LeSabre

My 1998 LeSabre has on three occasions failed to engage the starter.  No solinoid click.  Security light on for bulb test then off.  Has happened three times.  Intement lights come on all normal except no starter.  No effect by moving shift between park and neutral.  First two times I kept wiggling cables until it resumed normal opperation.  Three days later same thing.  Studied circuit diagram and factory manual (they arn't an easy study).  Swithed to a less worn ignition key.  Cleaned battery terminals and teminals on starter solinoid.  Last time it happened in my garage.  Hoping that I had the ideal failure (at home) we used a different car for the evening.  A couple hours later I got in to check it out and it started right up. With an intermittent problem I am at the point of starting to replace componenets and hope to get the right one early in the process. Anyone have helpful suggestions, experience or comments. My questions are:  Is it likely the relay, PASS key control or something else not that obviouse.  Also if it is the PASS key controler can I just ground the lead to the relay?  Given the car's age and the large number of white LaSabre's I don't really need the proteciton. Thanks for any info