i personally would advise to stay away from the 642 in general. i help run a shop and we see some of these every so often. they always have some strange issue. two have come in with the black death bad enough to torch a hole through the head past the injector face and require a new long block. plenty of issues with the timing chain and guides requiring replacement due to excessive wear before 200K but that was mostly up to MY2010. of course the Adblue system is problematic the tank heaters like to die and they wont cover it under warranty since its not the entire emissions system. and then theres the swirl flaps and the oil cooler seals.

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P