Before I deployed on this trip, I picked up a new water pump from Napa since my current one had sprung a leak and dumped a bunch of coolant on my apartment's garage floor (woopsy). When I looked at it, I noticed it has two mounting gaskets and a metal shim that matches up with the gaskets. I couldn't find any documentation in the box for it, so I'm wondering, what's the deal with the shim?

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me