Weedweater RTE115C grass stuck around string head - unable to see?

Weedeater RTE115C elec. grass gets stuck somewhere between string mechanism & head - took string part off & cover off head - unable to find anything - quits cutting during use. Has done this twice before. After sets for several month it must dry so can be shook out then works fine. How can I locate hangup at the time it occurs? Purchased 07/06. No service for elec lawn equip n this area.