We’re trying to mount the power brake booster to the firewall. We’ve got two different types of rubber boots here and one style has the thin gold zinc metal gasket. Both are said to be correct for this application according to NPD but they’re so very different. Both fit yet we doubt we’re supposed to use both of them, simultaneously with each other. The factory assembly manual nor the workshop manual we’ve got seem to be helping us. Please see the photo. Both seals are so different. Any thought as to which is correct? Thank you