sun vizor roller blind rear window E39

Since a few weeks my electric sun vizor roller blind for the rear window doesn't comes up sometimes. While pushing the button I can hear a "click" but nothing happens.
All fuses are OK.
After trying a week to pull up the sun visor, suddenly when I tryed again the sun visor comes up. In the BMW shop they told me that maybe the electric motordrive is broken and has to be replaced. The costs will be aproxx. 250 euro's / $ 200
I think if it's broken it won't work at all instead of sometimes it does !
Is this a matter of getting the electric motordrive lubricated....... (how do I do this, the device is hidden under the backseat-shelf) or is the device really broken and should replace it.
Has anyone else had this problem and how did he/she slove this ? Thanks in advance
Sharky (the Netherlands)
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