I'm in the market to swop out my 2017 GLC 250d which have served me very well and is now sitting on about 140 000km for either a GLC 300d with the new 2L and 195kw OM654 or another (also 2019) GLC 250d with the tried and tested 2.1L OM651 engine. When I took the 300 for a test drive I was slightly underwhelmed. I was expecting the newer engine to be quieter than the old 651 but it really wasn't. It was however quite punchy compared to the GLC 250 but seeing that I drive like miss Daisy that does not really worry me much. I have also read about some of the 654 engines having failing rocker arm bearings.

Anybody with experience of the reliability of the OM654. They have been available in the E220d for about 6 or 7 years now? All advice appreciated.

FIY most of the members here are from America, when we have few members from Europe.
The OM654 mounted in cars did not make it to this continent yet and 2023 is 1st year they are available here in Sprinters.
Meaning don't expect much experience with new engines here, so seek European forums.
I hear only good thing about new engine and rocker arms are small issue comparing to what OM651 had in its first years.
Good luck shopping.

Ahh, much obliged kajtek1!