I'm about to install an electric oven in our house to replace an
existing gas oven. The oven's installation instructions state that 8AWG
wire should be used to power with 40A breaker protection. Ok, makes
sense.

Here's the question: The oven has factory installed leads running out
of the oven via flexible conduit. There are two hots (a black and a
red), a neutral and a ground. The two hots are #12 wire, and the
neutral is #16! Is this safe to use, or should I re-wire to use #8 into
the oven? The leads are probably about 5-6ft runs.

Thanks!

-Eric