Molybdenum is best. What did they look like? The splines are where all of the Valkyries eat their drivetrain over time, mostly because most dealers don't even bother to check them. I'd look at the cush drive, as well. The little rubber bumpers dry and split.
After that, I'd check the u-joint and the output shaft for play. After that...
Look at the rear shocks -- I know a couple folks that bent the shocks and didn't know it. The rubber top shock mount inserts also go bad. Both conditions manifested themselves as weird vibrations.
Most of my off-the-top-of-my-head knowledge about 1500 machines is from Valkyries, but they're not that different.