usual story ... assembled as a unit, with zero thought given to parts replacement, like so many bits of kit these days
was exactly my thoughts
Not useful advice as such but I follow it often. "The slow way is the fast way", take everything off that you need to so you have good access. I use to like leaving as much stuff in place and working round it. Rarely is it ever faster and usually is a compromise when cleaning gasket surfaces or lining something up correctly to install. Way more to go wrong than being right at what you want to fix. Job's done right then. Unless of course you aren't very good at assembling stuff then the more stuff you take off the worse it'll go back together.
As I understand it you have one of the early jcb dumpers as Terex were building dumpers for jcb until 2017 so as said above some pictures would help. I am working on a Terex dumper for someone today so I will take a look but I doubt it is the same.