ST1200 Trimmer collects grass under bump head which bogs the motor down and gets shaft very hot. This has been an ongoing and frustrating problem with this weed eater for several years. I’ve since bought the 15 inch unit and love using it however I would like to get my old 12 inch unit working again to use as a backup. I’ve made sure everything is put together correctly. Just can’t stop the grass from collecting underneath. It only takes less than a minute for grass to collect. Any ideas or is this unit toast?