Folks,
Be very clear, the manufacturers only publish a RECOMMENDED TBO, there is nothing sacrosanct about the number.
For years before the "on condition" CAAP was published, most of the big commercial operators of PA31 etc had engine life extension programs, a typical extension for a Chieftain or similar was 2600 hours, and long term statistics showed NO ADVERSE reliability trend.
The enemy for seldom used engines is rust!!
Tootle pip!!
PS: The yanks have almost 100 years of experience, with 100s of 1000s of engines running on condition, including thousands of big radial in the days of piston engine RPT (likewise Australia), what more proof do you need.
Insurance company restrictions --- because they can, no competition in Australia, and they have been lobbied very heavily by those who overhaul engines in AU --- surprise, surprise. Believe me, LAMEs (with honourable exceptions) are not necessarily the experts on engine life.