Hi i just brought myself a version 6 sti it has 93000km on the clock and has had logbook services on time, its in due for service soon the last owner who had it used castrol oil.
What would be better to use a synthetic oil or a non-synthetic oil and what in your opnion would be the best oil to use , it has been tuned with a aftermarket ECU currently running 17psi on a stock turbo

thanks