Update: The tanks on hull
#83 are stainless steel
, and the sending is on the starboard tank. I checked while replacing starboard head hoses. (I haven't checked the port tank yet.) I removed the sender and it has two small posts - one covered in white plastic and the other not covered. There is a small break in the plastic (might have occurred when I removed), and some small rust like spots near the bottom. The sender has a number stamped on bottom of send head - 02 240 401, but I can't cross this to any spec. It appears to be the same physically as the VDO 226 453 you recommended in an earlier comment.
I checked the sender operation. When red/black wires are connected to the sender head, the tank gauge reads full. When removed the gauge doesn't move. I presume this indicates there isn't a problem with wiring
. So, now I have to decide to spend $300 for a new sender, or be more attentive to filling or running the WM.