Let me clarify a couple of things....salary isn't the best but not terrible, pension is matchd by the company up to 9%, roster is quite flexible and trips can be long or short to suit lifestyle, 18 days days work per month, fixed schedule with little or no adhoc work.
The reason that very few leave GSS is that the time to command can be as low as 4-5 yrs, the Ts & Cs are good, approx 400hrs per year so not too labour intensive and most importantly its a great company to work for.
Not to mention a 747 400/-8 type rating.