[twowheels]

The issue is clearly a QC one - the gasket surface is not perpendicular to the "cone" for the impeller. There may have been some attempt to correct this at the supplier (I too have seen some new covers with a half swath of tooling marks inside) but the aluminum impeller just got into it more.

You would think that if all else is equal the impeller would want to avoid the cover, but perhaps the pitch/sweep of the impeller blades drives it outward, or if the water pump shaft and gears aren't exactly parallel to the crank the water pump shaft may be being forced outward when the motor runs.