Not sure about cleaning up a solenoid, doubt it. Chances are higher it is the solenoid going bad and not the starter itself. If it were me, I'd troubleshoot it first, but replace both if it isolates to either. Could be your alternator is going south.
"Most vehicle starting problems are a result of a lack of current moving through the large magnetic coil of a starter solenoid.
When you hear a clicking sound but the engine does not turn over, the battery does not have enough life to magnetize the large coil and pull the plunger into place. Several things can cause this. In most cases, the battery does not have enough charge to power the solenoid because the headlights or other electrical component were left on and drained the battery's charge. Battery drainage can also be caused by short circuits in more severe cases. A lack of charge reaching the solenoid an also be caused by corroded battery terminals, loose cable connections or a damaged positive battery cable."
Read more:
http://www.ehow.com/how-does_5511222...#ixzz2vRTZRZVE