Not familiar with prewar senders but if yours is a straight resistance sender it sounds as if the phenolic resistance wire support is either warped or the wiper and wire is dirty so you have an increase in resistance at the spot it acts up. Warping is hard to correct so a job for someone who knows the process. If dirty, sometimes they can be cleaned by contact cleaner if the wire type but they are delicate. If it is the carbon deposit resistance type or the bimetal type then I would send to a professional for a rebuild -- if the cost of a rebuild is less than the cost of an exchange from one of our vendors..
If your sender is serviceable or reliable enough as is you can replace just the float and gasket. Max has the individual already cut gaskets for $3 and there are floats at some of the popular car vendors. Not sure what yours looks like or the dimensions but on the 47 I was able to use a repro 34 to 46 chevy pickup cork float from an ebay vendor -- $9.00. It was comparable in size if not identical to the one used on the Packard. There are different sizes available for other cars or years.
If you want to try modern and your sender is able to be measured reasonably accurately you might look at Classic Instruments
http://www.classicinstruments.com One of the posters on the PAC forum did not have a rebuildable sender to exchange so was able to find a modern replacement from them that would work on his car.
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