Ever get that shake when you are going about 50ish? right at the speed limit, the car transforms and becomes a rolling vibrator? well, you're not alone. it could most likey be your thrust arm bushings.
now conventional wisdom would suggest to replace it with OEM E39 540/M5 bushings however, there are some that went with an E38's bushing since it's said to be stronger (car's heavier after all). But I personally like the idea of using X5's bushings. It's not as clear cut as it seems though. There are controversy behind which bushings to use and even how it should be installed. The X5's suspension geometry is reversed and thus the bushing is installed reversed but what if you reversed a reversed bushing in ours? it's complicated so i'll get these guys do the explaining with pictures:
Bushing controversy..... and you thought "who killed JFK" was complicated... HA!!! they never owned an E39