DDK - Die Deutschen Klassiker

So, rattling door... investigate... regulator spring must have come off retainer.

Loosened four bolts, spring falls away. Removed.

Window works fine. Question. What’s the purpose of the spring? Am I fine without it?

The centre retainer for the spring is a weak point and breaks allowing the coil spring to come adrift. The spring retaining pin can be replaced easily. Having repaired two regulators recently with this issue, as far as I can see, the spring just provides some "asistance" on winding the window up. The regulator experts may chip in shortly and correct this assumption.

True.
The spring counter balances the weight of the glass when winding upwards, gravity assists when winding down.
The aim is to have the same effort winding up as down.
Seal condition has a dramatic effect on this ideal.

Many thanks. After oil and noticing the seals are new, the up down action is fine. I’ll just leave the spring out and enjoy non rattling door.