Angier,

To get to your original question,  yes the starter can fade away with time.  A number of things can deteriorate.  If it is a permanent-magnet motor (I think it is, but not sure) The magnets can become weakened.  This usually happens during a cold weather jump start when the booster applies more voltage than it should.  This can partially demagnetize the magnets.  The brushes can have resistance that increases with usage.  Adjacent turns in the windings can short to each other, reducing the output torque while increasing the current draw.  But as some suggested, increased resistance of the wiring is perhaps more likely.  The way I check that (after doing a quick check of all the connections) is to run a lead from the starter terminal and one from the battery positive lead to a voltmeter.  While cranking the voltage drop should be low - maybe 1 volt or less.  Then run a lead from the motor housing (starter motor, not engine) and from the battery negative lead.  The same result is hoped for.  If the voltage drop is up in the 3 volt range you have to find the source and one way to do that is to repeat the test with the voltmeter across various portions of the system.  But you likely won't find a singular loose connection - any loose connection absorbs a LOT of power during the event and will likely open up soon - it won't stay like that for a long time.  Hope this helps.

Gary Casey