Outdoor Power Equipment and Small Engines - Troy-Bilt 4-cycle trimmer troubles

My trimmer has the EZ Link attachment system and it seems that the main drive shaft is slipping. It runs fine one day and the next barely turns the attachments. Any ideas or links to where I can get a maintenance manual or is this a major problem requiring a technician? Thanks in advance.

The e-z link attachment system uses a spring loaded upper shaft which must engage the attachment shaft when inserted. Several have come into our shop and found that the coupler that holds the lower shaft to the upper lost the retaining screw and slipped down the shaft. The other unit that came in where the customer had removed the upper shaft from the engine and lost the spring for the upper shaft. Before starting the unit after putting the attachment on, you can manually turn the attachment and in most cases feel the attachment engage the upper shaft.