No pics here at work
I'll try and describe it ...
looking at the battery from the right side of the bike, on the left side of the battery is the earth terminal, with a right-angle bracket bolted to it with the bolt pointing up.
The earth wire which goes to the frame is connected to the bracket with a bolt pointing to the back of the bike. Except its not a bolt cos theres not enough space, so they splined a stud onto the bracket, and if you tighten it up the splines slide and you get a worse connection.
There is enough resistance on this connection alone when its bad to stop the starter working properly.
A new one isnt a fix, cos its just the same, and as soon as you tighten it its will get worse.
The solution is in 2 parts :
take it off, knock the spline back through a mm or so, centre punch the back of the stud, knock it back flush so it wont pull out again when you tighten the nut.
Then solder it up at the back (where you centre punched) to get a good electrical connection.
Of course, it wont fix a battery that is past its best, but it all helps