Basically, ECU are designed without assuming that lid can open.
I contacted an senior engineer who has been working with a world-class electronics company for more than 20 years and his reply was quite simple and I like his solution.

After several tries, we decided to use 2 methods in order to close the lid after applying a little of thermal grease on dedicated location.
so we can make sure the protection from heat and no water damage.  

• Using silicon rubber sheet to close lid.

• Using silicon gun and replicate factory shape after removing factory silicon sealing.   

 

Since the advent of the E46 and the late E39, the BMW key itself serves as a memory chip as well as an immobilizer. In general, the immobilizer has two or three hex codes in the key, and most of the companies have further programmed with VIN. BMW key itself is GSM It is used as a SIM (Subscriber Identification Module) card used in mobile phones.

Various information is stored in the key as well as the immobilizer. In simple terms, it is not only the time for replacing the engine oil and configuration of the chairs and radio and memory, but also stored the snapshot information by OBD-II and all the information received from the ECU at the time the warning light was generated.

source

“When BMW connect their PC on the car they quickly search if the car is modified.
If they see the DTC code related to a software modification you directly loose the warranty.
To not show this dtc you’ve two ways.

First, you can delete the DTC directly in the software (search 8209 in 16bits in the DTC area).
Or, better, you can correct the CVN to have the same CVN like the original car.

This second way is better because in Germany (for example) the CVN is checked by the MOT and or by the TUV.
If the CVN is the same as the original for the related VIN, they think that the car is not tuned.

But concerning the warranty is more complicated. If the ECU is not open, if the CVN is corrected don’t think that BMW is completely flowed. It exists FASTA. Behind this bmw name, there is a logging system what records all the interesting parameters like : rpm / torque / boost pressure ect.. If they have a doubt concerning the fact the car is original, they will look at this.

One advice. If something wrong with the car, put the car back to original first and if the car can ride, make some kilometers, FASTA will record orignal data and you can pray to keep the warranty.”

https://www.autotuner-tool.com/en/newsdetail/cvn-bypass-counter-patch

De lekkerste wegen van Nederland?