Original tension struts have fluid filled bushings...and bushings can crack and let that fluid out...
leaks look something like on the pictures in this thread:
https://www.e90post.com/forums/showthread.php?t=607239
Now you can put new oem tension struts with fluid bushings, or replace bushings... Buy aftermarket solid bushings...
or do what i did:
Replace them with e9x M3 tension struts. They have solid bushings that last longer and if i remember right are actually cheaper than tensions struts with fluid filled bushings..
M3 tension struts dont change your alignment/ camber. only difference is the bushing.
If you wish you can replace lower wishbones aswell with M3 parts. they give you more negative camber, have ball joint instead of the bushing.
Only problem with them is you have to fabricate/mod headlight level sensor bracket because m3, 3 series or 1 series have that sensor on the other side. not hard... original bracket wont fit all the way around the M3 wishbone because its alot thicker... so i used stainless steel cable ties to make it work... also ground a small notch to the wishbone so that sensor bracket wouldnt slide on the wishbone.
TRW makes these control arms for BMW so i would recommend to buy that brand. Lemförder is ok too.
FCPEuro sells a full kit:
https://www.fcpeuro.com/products/bmw...rade-bmwmcakit
This kit includes headlight level sensor rod aswell but on Z4 you cant use it.
Quick fcpeuro video on them aswell:
https://www.youtube.com/watch?v=pXwZ8t0Z0Ns
On the drips: You may want to check oilfilter housing for gasket leaks. Its usually the first thing that leaks on N54 and it leaks down the front of the engine where serpentine belt is and you may not smell it in the cabin.
Though when mine leaked i did not notice any oil drips on the floor...