Ian,
thank you for the really detailed information. This is my first boat so I'm a little new to this stuff. When I had it surveyed before I bought it the surveyor noted that the piece should be replaced due to the pink spots you pointed out. As well as mailing this group I mailed Jeremy Rogers and got a nice reply saying that if I send my piece off to them they'll have a look and quote me for repair or refurbishment. The item is in the post on the way to them now.
I can't remember what material the bolts were holding the housing on. When I took them out I remember they came out very easily and the holes were full of silkaflex type stuff. I hadn't considered the material of these before, well pointed out. I'll have another look before I attempt to mount the piece again.
Robert