Sir, It sounds like you have already done some troubleshooting and ruled out some possibilities. One thing to check is the foam seals around the film back, as these can deteriorate over time and let light in. It's also possible that there is a crack or gap somewhere in the camera body that is letting in light.
If you haven't already, try replacing the foam seals around the film back and see if that helps. You can find replacement foam seals online or at a camera repair shop. If that doesn't solve the problem, you may need to have a professional camera repair technician take a look at it.
In general, when troubleshooting camera issues, it's helpful to look for patterns in the images you're getting. If the light leak is consistently in the same spot, that can help narrow down where the problem might be coming from. Also, make sure you're using a consistent method for loading and unloading the film back, as any variations in how you do this can potentially introduce light leaks.