If you do decide to go JDM (replacement motor) in the future, Nippon Motors has them. I got mine about 40k miles ago and still going strong. Yes, I put the older engine in it in a newer Metro.
Nippon Motors
The engine prices have gone up since I bought mine 2 years ago - was $295, now $395. Still worth it since engine parts can add up when you buy them separate for rebuilding.