Sligh a little behind

Our 15 (approx.) year old Grandfather's clock with a Sligh moon dial movement consistently chimes 1 hour behind the actual time which it displays accurately. Ex. at 4:00 it will chime 3 times. It plays the appropriate musical chimes accurately on the quarter and half hours.
I'm suspect that there is a hand turning procedure, etc. to fix this but I do not know what it is.
Can you help?

Thanks,

Dan