T&T: Transmission oil

[bv]

Good morning

A neighbor boat of mine has a little Ford Lehman 46 HP (or so). No manual,
no ex-owner to ask to. He was wondering how to check the transmission oil ?
Does he need to have the engine running ? When the engine is not running, no
oil is appearing on the stick. Is this normal ?

On the other way, what could happen to a transmission if it is ever
overfilled with ATF fluid ?

Thanks a lot

Bryan