SO45.1 in-mast furling foil tension

[ubuysa]

I have a 1995 SO45.1 and it appears to me that the in-mast furling foil is too loose. At anchor I can usually hear the furled mainsail slapping against the inside of the mast as the boat rocks. Does anyone know whether the foil tension is adjustable and if so how do I re-tension it?