I devised a way to get v bands to seal without needing gaskets or silicone. In an ideal world the v bands are taken to a machine shop where they are turned to make them perfectly flat, then no gasket is needed. However if you have a leak, maybe because you just made up a new manifold or are replacing a part, it's generally not feasible or affordable to get a machine shop involved. So here is how to get the mating surfaces of your v bands perfectly flat with do it yourself tools.

You'll need the following:
A slow, high torque drill with 1/2" chuck. A low speed drill press might work if the parts are portable. I used an old Milwaukee 500RPM max hand drill
A lightly used or new 8" grinding stone from a bench grinder. Coarse works well.
A 1/2" bolt about 4 inches long with a nut and some washers
A tin of 30 weight oil.
Black spray paint

Make an arbor for the grinding wheel with bolt, washers, and nut.
Chuck the grinding wheel on the drill.
Take the first part with the v band and firmly secure it in a vise with the mating surface facing up.
Lightly spray paint the mating surface and let it dry
Oil up the mating surface of the v band and the side of the grinding wheel
Place the oiled side of the grinding wheel on the oiled mating surface.
Use the drill to slowly rotate the grinding wheel with very light pressure. At first use light pressure and spin the wheel at about 10 RPM. It might wobble a little, use less pressure. Eventually you'll be able to get the wheel up to about 60 RPM, using just the weight of the drill and occasionally adding more oil. Go lightly and slowly, nothing should get warm. Check the mating surface frequently and you'll see you paint remaining on the low spots. With patience, a light but firm touch and liberal use of oil you'll be able to keep the grinding wheel slowly spinning on the mating surface. Even with the coarse grinding wheel you'll see a perfect, professionally looking surface.
Slow, no heat, consistent pressure, oil, and you save the machine shop.

I did this on my new stainless hot riser in the vise, and did the turbine side while the turbo remained installed on my 1978 Perkins T6.354

Good luck,