The red stuff is the 518. The 517 is a purple color. Before I applied the sealant I first sprayed the surfaces with the gasket maker primer spray. From Loctite. With the first assembly I sprayed both half‘s of the case and the sealant stuck very well. On the second try After which I also had to disassemble because of the missed Gear, I applied the primer spray to only one surface as directed in the instructions. This made cleanup much easier the second time because the surface that did not have the primer did not harden into a plastic like film yet.