That is how the new parts come, but I guess it's possible to dismantle the assemblies and replace only the parts needed. That would mean getting a second hand assembly to do it yourself.
There's a HowTo on repairing the float/rheostat gizmo.
Click:
https://the75andztclub.co.uk/forum/s...d.php?t=194156
Unfortunately, it hasn't been recovered from the Photobucket ransom. Maybe there's a later edition somewhere?
TC