Moisture is not your friend
Rain, Spa's, Saunas, hot tubs, sweat box , sweaty sport activities and having your phone in your pocket close to your body without the benefit of a leather case will cause your woes to continue.....
Dump your phone into a bag of rice on a Sunday evening when your call demand is low--leave it on the charger if you must, but figure out a way to bury it in rice which is excellent for pulling moisture out over night.
You should have the ball replaced--the smartest way to do this and avoid the $39.99 or $49.99 most cell phone repair shops will stick you for is to find a old version of your phone at a thrift store buy it and take it into to your Blackberry dealer (if your not a do it yourself McGuyver type), typically they'll pop the new ball in if presented with both phones for free!!! ,
Voila you're rocking and rolling again!