There are no solenoids in a manual trans. It its grinding then the synchros are damaged, likely from miss shifts. You can try flushing the trans fluid otherwise the only fix is a rebuild.
Flush the trans, put some thicker fluid in it like Torco MTF, you will need buy 3 bottles. Oh and learn to shift smoother That isn't me being a dick. It is an actual piece of advice. You also could have popped the springs on your clutch if you are too hard with it during your "racer" downshifts.