boonyama,
Welcome to the forum.
If you click on the post "Fast moving parts" you can order a manual there.
There is no other info online for these mowers, this forum is it.
The oil drain plug is underneath the oil filter, facing down on the 6800, you may have to feel around for it.
Have a funnel handy, or it'll get all over your deck.
The recommended oil is 10W30.
Rattosh51
YT6800