Thanks for advice
I'll give soap and water a try. I've posted a mouldy writing picture, doesn't look worn or used at all, just dis-colored. Giullari label still on it too. It'd be a shame to ruin it so I'll take my time.
Seat came from a loft clearout via eBay, I'd been watching for a couple of years - missed out on the only other one I saw. Cover came up at same time, bizarre. Cost me as much as seat!
Seat frame itself in good nick, has wierd plastic knob and what appears to be a hinged flap at rear (one of photos) I'm assuming seat attaches, hinges over bike frame, tool tray etc as normal 400-four seat would.
There is a Giullari seat of sorts (not this one) on eBay at the moment. Not sure for CB 400 though, maybe CB 550.
Ha - sorry if this about the dullest post and photos sohc4 has ever seen!!!
M