Hmmm if my info is correct you Hydro Gear 21L pumps or at least that what the G2 service manual indicates. But I also seeing what appears to be an Eaton transaxle used. on some the 928D mowers. So I am a little lost here but basing the info on you saying you have G2 system.
Pay attention as one you are loosening. If I remember correctly the hex is a 5/8 wrench size.
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