How can I fix my grandfather clock?

It is 20 years old and won't chime on the hour, but chimes on the 1/4 hour, 1/2 hour and 3/4 hour. When I get it re-synchronized so it rings the 1/4 hour on the 1/4 hour, the half hour on the half hour, etc., it gets off by 1/4 hour again when it won't chime on the hour. I have oiled it according to directions, have made sure it is level on the floor and done everything else I was supposed to do, which I usually do when the time changes from standard to daylight savings or back. The only thing I can say is that changing it off daylight savings time last weekend messed it up some how. It never had messed it up all the other times in 20 years, so I'm really puzzled as to what to do.