Quit running as in seized?
Can you prove the engine has been serviced as required, with oil meeting spec requirements?
Sludge often occurs if the answer is no, in particular if combined with a majority of short trips.
Your engine (if it is a 2,3 Turbo) is dependent on good oil and correct level, due to the tiny amount in there. At least if it is similar to the Mazda 6 2,3 (only 3,3 litres IIRC), which is known to seize if the oil level isn't monitored frequently. They tend to burn some oil. And finally, there is a huge difference when it comes to the oils ability to keep the internals clean. I can confirm Castrol synthetic oils are extremely good at it.
1998 Xedos 9 2,5 MT (5-speed)
2000 Xedos 9 2,5 AT
2002 BMW 530i Touring stickshift
Originator of the Mazdaworld Old Boys Team!