I have over 280,000 miles (dont remember exactly) on an FE140 and it runs fine, now that the stupid exhaust gas heat exchanger has been removed
Gets 15-20 MPG (US) depending on speed and load.
I could not find Mean Time to Overhaul, B10 or B50 for the 4M50, but a call to the dealer may garner that info, since it can be difficult to obtain on the clear web.