Gas tank sender unit - Float won't float?

Late last season the gas level indicator stopped working on my Seca 550. Did all the tests, couldn't find anything wrong with the sender or indicator. Turns out the float no longer "floats"! I was able to get a reading by "fishing" for the sender arm through the open gas cap with a long bent piece of copper wire and pulling it up to make the meter work. The sender would not stay in the "up" position with a full tank, it just sinks, so it's not friction or corrosion at the arm pivot.

Anyone ever run into this one ? Fix should be easy but I find it odd....

 

may not be a solid float and can be soldered (brass) or sealed with gas tank epoxy

or float fell off of the arm

 

Yeah, those floats are a small plastic square and likely hollow, from what I recall (I've had the unit removed before). I don't think it fell off - I would have heard it rattling around in there when I inverted the empty tank while connected to the multimeter - I assumed when the multimeter showed a good impedance drop when I turned the empty tank upside down, that the problem wasn't in the sender unit. Little did I expect the float wasn't doing its job.