FYI, I spoke with an engineer about this, and he tells me the holes in the block for the fan cover/recoil starter studs are NOT tapped, but the studs themselves are self-tapping.
Further, the torque spec used to apply the nuts for the recoil is probably higher than the effective torque used to tap/install the studs, so, when you try and remove the nut, the stud itself will comes almost always come loose first.

I've had this happen on my HRX mower (less than 2 years old).
I'll mention this issue with our service guys...who knows, might get the factory to change the spec so this issue can go away.