If it is the motor spinning without engaging then just put a rebuilt bosch starter in it and be done with it. I do not do alot of white engine starters but I had one last week that sometimes the starter gear would not retract all the way after releasing the key and with the engine running you could hear it hitting the teeth on the flexplate, "ting ting ting". I fiddled with it for awhile trying to get it to duplicate and I found that intermittantly it would also do just what you are talking about. I would be standing there, holding the remote starter button down out under the hood, and the starter would be spinning like mad but not engaged in the flexplate so all you heard was the "whirrrrrrrrrrrrrrrr" noise of the motor. Sure it is probably a dirty connection inside of the solenoid but the reality is you need to just swap that sucker out and be done with it. It's kind of a pain in the butt to get that starter in and out of there but not too bad, just remember to disconnect the battery first and have your radio code handy.

Mark