Guess I should add that, I replaced the coolant reservoir on the Cayenne today, not too bad a job, considering the first instruction is remove headlight.
You need the headlight out to reach a bolt that holds a torque arm that holds the engine. It has to come out to get the reservoir out. In a feat of supreme German engineering, the bolt heads are 16mm, a size that doesn't exist in wrench or socket sets, you have to use a 5/8" socket on a long extension.
Anyhow, Mahle reservoir, $162 plus tax. Maybe an hour to change it at a leisurely pace. Seems ok now.
Dealing with the BMW leaky coolant expansion tank now - known to fail with age.
How does the Porsche one fail? BMW's is made out of 2 pieces glued together.... when it ages, it leaks along the seam all around. Around $100 - Mahle from RA.
Speaking of over engineering on the German cars... two piece tank (probably needed due to interior molding complexity), low level sensor, quick connect hoses (2), level floater stick (need to figure out how to read it)...
Looking at the Mitsu --- one piece see-through white plastic bottle, min/max lines, one hose with a metal clamp, no level sensor - you look at the tank and see the level. Probably will last forever.
With BMW, you have to open the cap (black tank, no see-through) and the little floater will tell yo the level if you know how to read it....
Now, truth to be told, the sensor will warn you if low coolant without ever needing to lift up the hood... Just like the oil level sensor (no dipstick).... The complexity does serve a purpose in some cases, but at a cost...