Harley-davidson Softail Or Dyna (v-twin Air-cooled Engine With Finned Cylinders, Chrome Exhaust, Black Powertrain) Common Problems

Known issues to inspect before buying a used Harley-davidson Softail Or Dyna (v-twin Air-cooled Engine With Finned Cylinders, Chrome Exhaust, Black Powertrain). What to check and how much repairs cost.