In an attempt to remedy what I thought was a carb issue, I began to use seafoam on a regular basis. Shortly afterwards my fuel gauge malfunctioned and would always reflected the tank being empty. I didn't think much of it because I know fuel sending units sometimes just fail. Today, I finally decided to order a new sending unit but before making a purchase I did some research and this is what I found.
Some of you may be interested in a problem I've had with a fuel sending unit on my 1700 Fisherman. Recently I added two cans (32 oz) of Sea Foam to my 26 gal gas tank (2002, Lund 1700), in an effort to help a carburetor problem - per recommendation of a number of Merc. outboard repairmen, and the local Lund dealer.

With a full tank of gas, I took the boat out two days ago and discovered that the fuel gauge read empty. I pulled the floor board and found the tank was full. I pulled the sender (WEMA model UFW 5.5, manuf date 3/13/02) and found that by manually moving the float, the sender was working OK. I then did a series of tests on the float with pure gas, gas diluted with Sea Foam and straight Sea Foam. I think that the Sea Foam lowered the specific gravity of the gasoline and the float was not able to displace its own weight with that additive in the gasoline. The result was that the sender's float apparently sank in the gasoline with Sea Foam added. Evidently this is caused by the plastic material will not floating correctly with a Sea Foam additive.

So, I've decided to purchase a replacement sending unit from WEMA that uses a stainless steel float. I've not received the new float yet, but will follow-up with a post when I get it installed. Hopefully the stainless float will not sink in the gasoline with Sea Foam additive. By the way - WEMA USA is the manufacturer of the sending unit and they have been great to work with, nice folks, good service.
There is no certainty that seafoam is the culprit but I thought it to be a heck of a coincidence that I had the same exact experience. Hopefully the new stainless unit will be more durable.