If you are talking about a French car the float is skewered on the metal arm.it can be removed carefully and replaced with a quality cork – I have used Moet and Chandon Champagne corks, but, realistically any cork should do. You can try sealing it with araldite type glue although it never seems to work completely. Consequently it has become a yearly replacement ‘service’ item for me as the cork over time becomes porous and sinks. See my bit in Floating Power V0lume 43 Issue 2 page 7 March/April 2019. Never found a proper replacement part – all available plastic floats don’t seem to have the skewering method of fixing onto the arm.
Peter