Any 2000s BMW experts here?

2003 Z4 3.0i is about to hit 70k miles and, as one would expect, the coolant reservoir appears to have a small leak. I expected this when I bought the car, and it’s a very small leak and I have other vehicles so I can procrastinate a bit. Been doing some research but still have a few questions:

* There seems to be no consensus on what brand to use as a replacement. Lots of “don’t go cheap or you’ll have to replace it twice” posts, and lots of “stick with OEM” despite the fact that OEM clearly has a manufacturing defect. I searched but can’t find a metal replacement, and most of the replacement brands are either brands I have never heard of, or brands I have heard of but never with respect to cooling systems (HELLA). Any suggestions on either a part that actually solves the leaking issue or the best bang-for-your-buck option?

* When the coolant reservoir is replaced, there seems to be two groups of people. Group 1 just replaces the coolant reservoir, and Group 2 also replaces the water pump, hoses, sensor, fan clutch, etc. What is the failure rate of the non-coolant reservoir parts? I know the plastic water pump impellers are prone to failure, but nobody ever states an expected lifespan. I’m fine sucking it up and dumping some extra cash and labor in the car if it will last me another 50k, but if these parts aren’t prone to fail before 120k, I’m also fine enjoying a few more years of not dumping money replacing perfectly good parts - especially when replacing the water pump requires detaching motor mounts instead of and jacking the engine up instead of just removing a belt and a couple of bolts.

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Thank you!

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