When you find the line you might want to etch it a little bit deeper or wider so that it's easy to see. And worst case, talk to a
yanmar distributor, or order a new one. Though the info has to be in one of the
manuals, even if but in the big mechanic's only version.
You can also drain the fluids, refill things with the specified amount, & see where that brings things to on the dipstick. Though keep in mind that there are a few setups out there where you actually are supposed to check the level when things are hot. As in it's been running recently.