Wow, I am amazed that you actually let a mechanic touch your car (unless I trust him or I know what he is trying to do). I personally would never ever do that but then that's just me.
Engine dies at 40,000Kms? The guy was either tripping on acid or he's just plain retarded. Didn't you ask why the engine of these 'Japani gariya' die out at 40,000kms?
That's the same case that happend with Mazda RX-8 which local 'dealers' and so-called 'ustaads' started. They said the rotary engine of the RX-8 dies out at 40-50,000kms. Which is total bs, the rotary engine needs care unlike every other engine but yes it needs some extra care. Hell every sports car needs extra care to make sure it runs like it should.
Anyways, now the reason he said this is that a huge majority of people that buy JDM vehicles don't maintain them at all. JDM vehicles don't require much work except your regular check-up. Now when they're completely battered the sheet out of by their owners they go to these so-called 'ustaads'. These 'ustaads' don't know jack-sheet about ECU based engines or in their language 'computer wali gariya'.
Since they're use to fixing carbureted engines and that's all what they've been seeing and working on since they have started working on vehicles.
If you're facing a problem with your car get it scanned with an OBD-II scanner and get that problem diagnosed according to the errors that show up on the scanner. Don't take your cars to your local lalu, pappu or whatever the hell they're called. I've heard a lot of stupid stories with mechanics screwing up pretty good engines.