1. The sure test to determine if this is an oil pressure problem is to attach a pressure gauge to the engine checking to see what the actual pressure is when the light is on. A little tricky to do given the location of the sender.
2. It sounds like you are using the proper viscosity of oil so that shouldn't be an issue.
3. Also, if it was worn bearings, the oil light would usually come on after the engine got hot (oil thins).
4. Another item to check is the wiring harness to the sending unit. The oil pressure sending unit provides a ground for the light at low pressure so if the wiring harness is contacting the frame and grounding out, it will turn the light on. A loose connection on the sender does nothing. This is for the Roadster. I'm assuming the oil light circuit is the same for the Touring.
5. There is a way to check the sending unit, once removed, with a small enerpac hand pump and ohmmeter. Hook the ohmmeter up between the sending unit body and terminal. Should have continuity at rest. Slowly pressurise the system and see what pressure the circuit opens. I think you could do this with a small compressor and gauge also.