tim,,,my guess is the shifting linkage seal needs replacing,,fluid level goes up as it sits and can reach the seal leveland if seal is worn or just plane old they can start to seep fluid..,its not a hard fix,,drop trans pan ,disconnect linckage,,drop valve body,seal is in the shaft hole,,knock it up and out ,,new seal in hole and down,,reasemble with new filter as long as your in there,,takes 1 to 2 hrs for all of it,,.rick