The Triumph Stag as far as I know was so poorly designed that regardless of how well you took care of it, it's engineering flaws would starve the engine of oil and grenade it. An engine swap would be your only cure. Toss in British manufacturing o the time, and you have a winner (loser). Generally any car will be okay i you take care of it, even a Chrysler 2.7. But this car was doomed from the get-go.