If your Moulton is the Raleigh production model the tubes connecting the rear wheel used to fracture where they joined the rubber suspension, point of high stress behind the bottom bracket.
I have a dye line print of the original Moulton patent from 1958 which is close to the later model that Moulton produced, rather than the Raleigh rather poor attempt, nothing like the original design.
Although I didn't know at the time I built a pair of wheels for an early experimental one. Also I used to see Vic Nicholson when he was working for Moulton as professional rider. This would have been from late 50s and he was using a frame similar to the raleigh, with the suspension very stiff. More or less proved for me that there was no real advantage to small wheels, but worse over bumps, and absorbed energy.
