@ pso-buzz.
No, there is a way round it, Phil's ULA replacement. Look at Phil's article at
http://www.cypax.net/projects/ula/index?language=en, you will see that Phil produced a unit that simulates the original ULA.
This unit is not a direct replacement for the ULA but with some slight mods to the C5's electronics it would bring the C5 back to life, plus with some additional components the C5 could be used in pedelec mode.
I offered some time back to produce and test some of these units if someone in the UK would be prepared to program them for the customer and distribute them. Due to lack of concrete help from the UK side I've now dropped the idea.
I'll produce a unit to convert #1 to pedelec, and if Pat's unit is duff I'll go 24v on #2.