I found this extract in the depths of the Yanmar 3GM30
"Aging, breakdown and cracking of Fuel
Since the diaphragm
is constantly in motion, the cloth on its flexible parts
becomes thin, cracked and sometimes breaks down after long periods of use. A broken diaphragm causes fuel oil
leakage and fragments of the diaphragm often contaminate the engine oil
In my case at 750hrs (or 9 years) and fuel oil leakage = 3.5litres of gas oil in the sump!