Are ford focus st's reliable when kept well maintained?
No. Ford doesn't know how to make small cars.
What do you mean?
This question has been asked before:
https://carkiller.com/scottykilmer/qa/focus-st/
To sum it up, I wouldn't buy any modern Ford passenger car.
Also, the ST has a 2.0L Turbocharged EcoBoost Gasoline Directed Injected engine and the Wikipedia page has a whole section on 'reliability issues'
This alone would make me run away from it.
But didn't the st have a different motor and transmission?
Data suggests it’s renowned for reliability issues. However, if you want to look past them, and buy the car because you must have an ST, go ahead. Just don’t say we didn’t warn you.
For long term reliability and ownership, if you care about that, I would look at something else.