gpap123,
I've been doing so investigating and have found that 10W-30 engine oil should be just fine in the 763. I found this posting on a site from a 763 owner:
Was going to try and scan the page out of the service manual but unfortunately it had other ideas.
Under fluid type it says: Bobcat fluid (P/N 6563328); if fluid is not available, use 10w-30/10w-40 Class SE motor oil for temperatures above 0 F(-18 C)
5w-30 motor oil for temperatures below 0 F (-18 C).
That's good enough for me, and works just fine in my 763, but if your not comfortable using off-brand oils, use the Bobcat stuff. Me, I'd rather save a few bucks and put it towards something I enjoy.
As you can see this guy is a 763 owner and is using 10W-30 engine oil. I would recommend a synthetic 10W-30 API SE rated motor oil. I know over in Europe you folks have been running synthetics for years, so there are probably so good products available over there for you. I've never tried to ship AMSOIL to Greece, but bet I could get it done if you had not other options. Let me know if you can't find a quality 10W-30 API SE rated oil for your machine.
Thanks,
John