I think saw that a couple of weeks ago when I went in for some Yamlube..... Nice rib!
TBH it sounds like all your rubbery bits have hit their life expectancy simultaneously, which is why I replaced absolutely everything rubber on mine whether it needed or not when I rebuilt it. That flavour of engine is a bit of a servicing PITA, as the diaphragm (£4 worth on the 60) needs a complete exhaust side removal, to get at it so there's 12-16 probably rusted solid bolts' worth of time and two gaskets to add to that £4..... The other bits are a likely similar story, as those engines were remarkably light for the horses, but mostly because every compoment does three jobs!
There is another way of looking at it - For sub £2K are you really
likely to get something of 100 gee gees that is in a better condition & known history? In short, that's why I rebuilt mine.... Difference is for £2k you'll get it back this side of next christmas