My Hanewinckel 5-string has an oil finish, and Pete suggested using
Howard Feed-N-Wax. He says it can be applied with a Viva paper towel, then remove about 20-30 minutes later with a clean Viva paper towel. My bass has an Alder body with Walnut top, the neck is Maple, and the fingerboard is Pau Ferro. I probably won't touch the fingerboard, but the neck and body may be getting a coat soon.
On the neck, I'm also planning to gently rub in the Feed-N-Wax using a piece of 600 grit sand paper (Pete's suggestion if I'm comfortable using the sand paper).