Identifying a small part please...

[enuff_zed]

So when the time comes would you guys recommend having it towed to a mechanic instead of driving it there?

I think the ring maybe reinforces the bushing, makes it stiffer. The thicker side of the bushing is pointed towards the inside of the car, where the bushing gets it's forces from the suspension.
So maybe your bushings are quite worn (they are a wear item) and it's time to replace them.
Towing to the garage is not necessairy, and neither is stopping to drive the car imho.
But maybe time to find a good indy and buy the bushings online for a decent price (you can also opt for Meyle HD or Powerflex if you want a stiffer bushing with more lifetime; otherwise go for Lemförder branded, they are the OEM).

For people who don't have a clear picture where they're situated, here's a highres pic where you can see them sitting inside the rubber bushing:
http://buyparts.co.kr/shop/largeimage.php?it_id=1438329061&t=3

Yup that makes it clear. Looks like they're designed to stop the bush moving too far in one set direction. Therefore, if being put back in (even just temporarily) they would need to be located the correct way round. From the picture it appears it would be possible to install them 180 degrees out.

 

[GuidoK]

I've no experience with putting them back (I have powerflex in that spot) but as suspension parts are always under tension I can imagine that it's not as easy as it sounds (at least not with the car sitting on it's wheels on the ground).

 

[ydkcioc]

Thank you very much Guidok, it is very informative!!

 

[ydkcioc]

Looks like the spacer from inside the lollipop bushings.

https://www.realoem.com/bmw/enUS/part?id=BU52-EUR-03-2006-E85-BMW-Z4_30si&mg=31&sg=05&diagId=31_0642&q=31126783376

Hi guys, had both sides replaced today, I asked the shop to show me the old parts and confirmed all is true & honest. Thank you very much everyone!