just bought rockola453-need advice please

i have just bought a rockila 453 not in bad condition,but it seelms to
have a selection button problem,ie the 1st 2nd digit are selected
ok,but in the third the button is depressing but not responding to
select however when i hold the 3rd button and manually move along the
solenoid arm it does make my selection,the third butoon was sticking
sometimes and
sometimes the selection disc would just rotate and not make the
selection
regards
keith