If you use synthetic these are the change intervals according to HD (note the storage for winter exception):
Synthetic Motorcycle Lubricant has been tested and certified for use in all Harley-Davidson transmissions and the following Primary Chaincase applications:
• ’71-later XL, ’83-’84 XR 1000 models, and ’84-later FL, FLT, FX, FXD, FXR, and FXST models with wettype diaphragm spring clutch.
All Big Twin:
Crankcase: Replace after first 1,000 break-in, then every 5,000 thereafter (unchanged)
Primary: Replace after first 1,000 break-in, then every 10,000 thereafter or prior to winter or
extended storage periods
Transmission: Replace after first 1,000 break-in, then every 20,000 thereafter or prior to winter or
extended storage periods.
http://www.guillermo.ca/images/rk/PAB849.pdf