For starters try cleaning the fan. Get a can of this stuff and thoroughly douche the fan, not just the blades. Try to get the stuff inside the motor. You may have to remove it from the bike.
https://www.amazon.com/CRC-05103-Ele.../dp/B000BXOGNI
You must also replace the rear rocker box seal. The seal is made of silicone. Temperatures in the left rear corner of the rocker box sometimes exceed the seals rating. When this happens the seal cooks, loses its elasticity, becomes hard and stops sealing in the corner, (happened on both my bikes).
When you remove the rocker box cover you'll see an aluminum flange on both sides of the seal. The flanges form sort of a groove that the seal sits in. There are flanges on both the cover and cylinder. Coat the interior and exterior flanges on the cylinder and cover with Hylomar sealant. Now it doesn't matter if the seal leaks or not. The Hylomar sealant will hold backl the oil.