Me too, Phil, I recently spent 45 minutes looking for the transmission dipstick on my new pickup, there isn't one.
I thought for a while that the world has passed me by, is now confirmed for sure!
My understanding on Yanmar GMs
On GMF's (fresh water cooled) with heat exchanges. No anodes.
On GM's (raw water cooled) Yes anodes. One each cylinder.
On my 3GMC , raw water cooled / C= saildrive there are total 3 anodes (zincs as I call them) 2 along side of motor, under exhaust manifold, (one is behind secondary fuel filter) and 3rd is mounted on end next to exhaust elbow.
For saildrives, in addition to external lower, there is an anode up on side of SD.
Opposite side from water intake up high near yellow oil fill cap.
Not all are aware this one exists.
Is an adventure to change them!