Stainless steel that contacts Aluminum will corrode. It's not the same color as rust, but they lose their nice bright color and grow this gray-ish looking stuff if they are in direct contact with Aluminum, like an aftermarket intake manifold.
Sounds like marraige...
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.