Im like extremelow and run the Mobil 1 v-twin but make sure its made for the v-twins and not just a car oil.
This is directly out of the owners manual.
" Engine oil is a major factor in the performance and service life of the engine. Always use the proper grade of oil for the lowest temperature expected before the next scheduled oil change. Refer to Recommended Engine Oils. Your authorized dealer has the proper oil to suit your requirements.
If it is necessary to add oil and Harley-Davidson oil is not available, use an oil certified for diesel engines. Acceptable diesel engine oil designations include: CF-4, CG-4, CH-4 and CI-4.
The preferred viscosities for the diesel engine oils in descending order are: 20W50, 15W40 and 10W40.
At the first opportunity, see an authorized dealer to change back to 100 percent Harley Oil."