Hi and welcome to beoworld.
Replacement drivers are no longer available for the C75's although I have heard of someone using CX100/50 drivers with decent results. Refoaming is the way to go with these if you want to keep the original sound. Replacing aging capacitors in the crossovers will also improve the sound to original spec's.
The sound should improve after refoamig but this depends on the degree of degredation in the originals as to how big this will be. Either way the foams need rplacing as using them in the current state will probably result in the drive coils being ruined due to friction and then you're well & truly goosed.
Chris.
The use of metaphors should be avoided like the plague. They're like a red rag to a bull to me.