I has two sets of the Oregon G6 Gators. I'll see if I can dig up the part numbers.
I think this it: https://www.oregonproducts.com/en/gator®-g6™-blade,-20-1-2"/p/396-810
Oregon has a storefront on Amazon:
I'm not expert but I won't let that stop me from sticking my schnozz in.
Hydrostatic drives are closed loop. But since we don't live in teh perfect world some fluid leaks out of the system. The charge pump makes up that leakage.
I think it's good that your noticing only a small amount...
Closest I can relate to is when the woman in my life starts to revert to her Amazonian ancestry and I politely remind her of the vast catalog of grooming products/equipment in her lair.
I'm batting .500 on that front.