Spedometer stuck at 20mph when car is turned off and parked

Hello i own a 2003 chevy cavalier 4 door sedan with power locks but not
electronic instrument cluster panel. my spouces car however ;
today she discovered that the needle is stuck at 20mph and would not return to the zero position . i requested that she tap the general area to see if its just moisture or residual pressure perhaps a brake bleeding could diminish the cable pressure? the car has over 100k in miles and purchased as is. it ran well for 3months and just had a few minor problems i could deal with. do you think the spedometer cable is getting bad or the spedometer unit is just old and needs to be replaced ? is their a solution
that may repair or correct this problem. can you point me to a location or site where a easy solution may be found.

thank you all for your assistance
michael m.