It really depended on the bike, for most it was new heads, and the newest todays head gasket. For some it was liners in the cylinders moving as well. Was the recall ever done on your bike? If so you maybe you can find out if you got the newest head gasket when they did it or just one of the teasers that brought you back in again. The other thing that was changed was the compression releases the new ones seem to stay in much better

One other thing you may want checked when they do your head gasket it was a lot o fthe 07's did not have the rockerboxes clearanced properly. Harley did remedy this either by taking a dremel / or or other tool and grinding them down, or depending on when you got your bike they released new rocker box bases that were pre clearanced as the orignials shoudl have been. This caused an annoying ticking noise.
You can go on harley's site and put in your vin and check if any recalls are available for your bike.