Hmm Bruce, I think you might be onto something. I bought this mower with a flat idler pully installed and when I replaced it I asked an ex greenfield dealer for the part and that's what they gave me another flat. After doing a bit of research the part i need is a gt7965 according to the manual which is a v. However when I check my other 17 hp 32 inch fastcut it uses a flat pully as well.
Googling it shows both flat and v pulleys for the idler pulley so now im confused.
Ive given it to a repair mechanic to look sort out as Ive sunk 8 hrs into already but ill post what the outcome is within the next week.