It takes a lot of skin and a lot of sun to get your optimum dosage of Vit D. It is formed in the skin by UV-B rays acting on cholesterol to form Vit D3. There are several forms of Vit D - the cheap kind is made by the action of exposing plant sterols to ultraviolet radiation, resulting in Vit D2. D3 is an animal-based vitamin, which makes it better for animals right there. But it requires further processing in the liver and then kidneys to become available to the body.
If sunlight intensity is low, I fail to see how rubbing even a few capsules of Vit D3 on the skin (greasy?) would become an advantage over swallowing one or 2 capsules of D3 orally and digesting it. If digestion is at fault, correct it first. People living in northern temperate zones have to store enough VitD through sun exposure to get them through most of the winter. Most do not and cannot. Therefore, it is simple insurance to swallow a couple 5000 unit capsules a day for your health.