As it seems, the cost of spare parts and labor to fix the engine of my recently bust FZ6 engine are well beyond EUR 4000, so there's no point in repairing it.
As it further turns out, the previous owner of the bike (I bought it in April last year) had forged some signatures in the service booklet, i.e. the motorbike has likely not seen the regular inspection and service like it should. Haven't yet decided whether to file any claims against that previous owner or not.
Now I've decided to buy a new one of the same model, and keep the old one for spare parts. At some point next week I should be the proud owner of a brand-new FZ6 Fazer. With three full years of Yamaha warranty. Hopefully this one will live longer than 17,000 kilometers.