Looking closer at my drivers side strut tower from underneath as well as the original gasket, it's apparent that the clamp load isn't uniform around the entire surface.
The outboard bolt hole (top-right hole) has less gasket material transferred than the two inboard holes, possibly indicating less clamping pressure.
180deg opposed to the outboard hole is a keyhole cutout of the sheetmetal for some reason, and outboard of that is a witness mark that looks like some dirt rubbing against the sheetmetal (the light brown mark right at the edge of the flat part of the tower). This could indicate a gap allowing dirt to enter then relative motion between the two surfaces causing the brown mark.
Looking at the gasket, there's some small dirt particles stuck to it in this same area, and only this area, the rest of the gasket and tower surface are clean as can be.
Seems at least plausible that the top mount is moving or pivoting about the axis created by the two bolts that have the darker green gasket material around them.
Interestingly, the passenger strut tower's bolts are rotated a bit compared to the drivers side to make room for the negative jump start post . . . they aren't perfect mirror images. So the load path and clamping deficiency that would cause this issue are going to interact differently on that side of the car.
This would mean that the integrity of this joint will be highly dependent on torquing procedure, bolt stretch, and the load mitigation capability of the suspension itself. All things that lead to aftermarket parts (or even non-factory installation of OEM parts) potentially causing problems.
With all the aluminum in this suspension, replacing bolts when specified and torquing to correct specs is absolutely critical for proper performance.
Anyone have any ideas for how to test for relative motion between these two surfaces or fix it either temporarily (to verify the root cause) or permanently?
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