RB67 light leak identification

I recently discovered my RB67 leaks. I almost never take it outside. Based on the location of this leak, where should I start looking to fix it? The film path is quite complicated. The image is upside down in the camera, so I think the leak is on the left side, but I don't know if it's leaking round the flippy door or where the back fits on the camera. Do RB67 backs have felt that can go bad?

The RB has a thin fiber seal between the plastic top plate and the metal shell. The leak is at the left edge of the wind lever or close to it.
Get some black silicone rubber sealant. Remove the screws holding the top on, they are around the perimeter, lift the plate up and put a very thin layer on sealant on the existing gasket and reinstall the screws. Only snug the screws until all screws are started then tighten starting at the center working outward in a X pattern tightening all screws equally.
Test with ISO 400 film. Too much sealant will interfere with the mechanism.

It's the film back almost certainly, it's almost always the film back. Take the back off and inspect the screws to see if any are missing and all the corners to see if a bit of plastic has broken off etc, might be very well.