BTDT too - as
Clavurion has stated, they will all fail sooner or later.
Probably sooner...
I used the
X8R cast replacement from the UK. Pretty good quality and not very expensive.
I think there's a couple of different versions of these available (from various vendors) and it pays to check you get one with the correct sized exhaust ports - the M57N has slightly larger exhaust ports on the head than the earlier M57 engine.