The Type F is becoming hard to find on shelves.
That Amazon listing is odd as the gallon product isn't Type F. It's a synthetic I haven't seen.
I'd bet the 2 for $15.98 is the only Type F deal there.
I found a Valvoline 6-pack of MerconV on Amazon for approximately that $16 price not too long ago.
So another mistake. It almost seems like they do it on purpose. Walmart, Zoro, Amazon,. I guess this year if the price sounds too good to be true, it probably is.