It depends if fuel is leaking from the bolt under the fuel bowl or fuel is leaking from the mixture screw thread.
Options 1, fit fibre washer under bolt. 2, replace mixture screw and bolt or replace internal o ring (if it has an o ring that can be replaced) 3 ,If it's a small amount of fuel that is leaking, permatex gasket goo on the thread should stop the leak. 4 ,Stag sealant on thread and under bolt will stop the leak although you would have to count the number of turns to get the mixture screw out then put some stag on the thread and install to the same number of turns then once the stag hardens you would not be able to adjust the mixture without breaking the the seal you have on the thread.
