[Piper1]

Welcome to the community.

We really do need a Non M buyers guide on the boards to answer some of these as well as other reoccurring questions.

To piggy back and answer some questions as said, unless you get something that was just totally abused you shouldn't have a need for a rebuild, both the M54 and N52 are very solid and have less maintenance concerns compared to the S54 in the M. Like any BMW valve cover gasket, oil filter housing gasket on both are very common and like any car cooling system and tune up/coils/plugs and basic odds and ends as needed.

I have a '07 3.0si coupe 34k miles and a '03 2.5 modded with the M54 109k miles as well as a 2011 128i 105k miles 3.0i non converted.

The M54/N52 are I'd say equally reliable with their own quirks but more quirks are noticeable in the pre vs. facelift in the over all car. If you get a N52 3.0i in comparing my 128 to the 3.0si coupe you'll want to make sure you either convert the 3.0i to SI or get a SI, there's a major difference comparing and the SI is well worth it and plenty of write ups out there to detail how/why.

Biggest thing I miss in my 03 vs the 07 is higher revving N52 when comparing just the engines.

Prefacelift:
PCV systems prone to collecting moisture especially if just driven short distances will create the valve to clog, milky oil similar to blow head gasket signs but easy/cheaper to replace the PCV system.

Facelift:
recall on the PCV heater which was designed to combat the issue in the M54 PCV also N52 PCV system integrated into the valve cover little more work and cost in replacing the PCV system in the N52 than in the M54. Short trips still can cause moisture in the N52 PCV to collect so the heater doesn’t cure the problem entirely.

Prefacelift:
rear springs notorious for breaking

Facelift:
ABS unit motor failure from inline change on ABS motor

Prefacelift:
TPS is gauged by tire revolutions not by sensors in each wheel so it’s easier/cheaper for aftermarket wheels.

Facelift:
TPS in each wheel and periodically needs replacement and added to aftermarket wheels or you get sensor error light if not tuned out but is more accurate of sensors than the revolution sensors in prefacelift.

All Roadsters can have issues with motor for soft top if water collects in the drains if clogged. Either clear the drains as a maintenance or relocate the motor to the trunk.

So it's not really one being better/more reliable than the other, but different with their own issues and quirks, to me you can't go wrong with either.