The most plausible explanation for TN engines not making TBO while the same engine as NA version routinely makes it would be the operating pattern
May I add some information based on a Arrow 3 Turbo expierance. It is well established in the USA, that you will only get around 1260 Hours before compression pressures drop below acceptable levels.
This is generally put down to using Max Power settings on Take Off, of 41" MP and Max Prop. By reducing if runway length available to Take Off settings of 35"-37" MP and Max Prop, will allow the engine to reach close to it's TBO of 1800 Hours. At sea level it normally increases the Take Off run by 100 metres max.
The only thing I had heard against the T Tail is that on Landing, control effect is lost by lack of air flow over the elevator, on the Arrow 3 the prop wash maintians control, given that most people land an Arrow with a trickle of power to prevent sink.
Hope this helps.