thetford cassette toilet c2 leaking?

the c2 fitted to my campervan is leaking some where as the floor is very wet, dosen't smell so think it is coming from the flush tank. the cassette housing underneth is dry so dont think its a seal problem.
Could it be the tubing to the flush that is cracked and how do you get at it ? also the knob that opens the blade is very stiff to turn on the cassette it slides open quite easily.