When in hammer mode, the drill seems to hammer/chip until the unit gets hot. It then stops hammering. Everything sounds like it's hammering but it stops performing. I've put the unit down for 10 min and it works again but it's not always the case. Seems to be an intermittent problem. The brushes look slightly worn with no cracks or wire showing. I've taken the unit apart with grease everywhere on the inside. Looked at the o-ring fix on a previous post but it seems to be in good condition. Not sure what to look for at this point with all the grease and would hate to put it back together just to start over and break it down again. Tool has had some heavy use on and off over the last several years. Any help appreciated.