Exhaust Stud Leak at #8

I dont use silicon anymore. Try FIPG instead, its so much better.
https://www.amazon.com/AISIN-AB1207B1-Black-Gasket-Sealant/dp/B01MUFWSBH/?tag=fabo03-20
For your issue I would probably use indian head gasket shellac. Its great for sealing threads.