I get the feeling you either have bad luck with turbo'd cars or are ragging the **** out of them expecting them to perform way above their safe limit.
The scoobs and celicas are made to run UNDER their max power limit for safetys sake by the manufacturer. We can get a bit more out of them and use that safety zone a bit. BUT unless you start to change internals, if you run them at high speed for prolonged periods, you stress the internals beyond their capabilities.
The rally engines we built could take the extra power output, (most of you guys are running MORE than a rally car anyway!) but could do it for prolonged periods. Never-the-less, these engines were rebuilt after a few HOURS of work not MONTHS or Years!!
Track days are hard on the engine, but noone does track days EVERY day either. Loads of factors play in whats happened here.
Oil changes? Cool down periods? warm up times? what did the previous owner do?
When i sold my EVO6 to someone, they said they had bought another one and it blew up within weeks.
They found out that the previous owner had turned the boost up, ragged it and got the stratings of failure. so he put the boost down to lower than factory and sold the car! this poor guy bought it and ran it, turned the boost back up to factory and POP!!
i echo what i said earlier, too many variables too many things that can go wrong.