starting problem

car starts fine almost every other time, when it does not you can hear solinoid click no start, had corrosion at batterie terminals, cleand terminals and replaced pos and neg cables, checked battery, replaced starter solinoid does the same thing, I must be missing something any suggestions? just bought the car everything else works great

Disconnect the ground then pull the starter. Then hook it up electrically reconnect the ground. Have somebody else try to start the car. Watch the starter closely. Make sure the bendix is working properly.
You also can tap the starter with a hammer if it starts you need a rebuilt starter. Sometimes they get a flat spot.