Folks,
Long time ago, now, but we always fitted warm air filters, where available, either as an OEM option, or an STC.
I was always impressed with the difference in an engine at overhaul in the UK, vesus Australia, we still had warm air filters there, but there was never anything like the dust we got in our VH- aircraft. Indeed, in western NSW and FNQ we often did filter and oil changes at 50 hours, for air filters, sometimes less, depending on how fast they loaded up.
UK versus AU certainly showed up in overhaul costs.
Tootle pip!!