The sealant you want is Loctite 598.
Available in a 300ml caulk tubes or small squeeze tubes. In the US, Permatex Ultra Black is the same product. In additional to not being monkey butt orange, it is remarkably tough, oil resistant, and has a good temperature rating.
It's not hard to understand what you want to accomplish, which is to make sure every molecule of cooling air (1) remains in close contact to hot parts, and (2) actually gets to the hot places.
A light bulb held under the engine will highlight gaps.
The problem with wraps is usually air leaking from the sides, which means it does not cool the area around the lower spark plug. There are a whole lot of fins down there, but they won't do you any good if the air gets sidetracked.
BTW, Lycoming places a rubber comb between the fins, which blocks some flow and often worsens the wrap fit problem.
Along the same lines, engine shops often add a bead of silicone across the baffle in an attempt to stave off chafing wear. However, if the silicone is up between the fins, it blocks flow.