sun vizor rollerblind E39 won't work

Since a few weeks my electric sun vizor rollerblind (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 rollerblind, suddenly when I tryed again (while driving) the sun rollerblind comes up. In the BMW shop they told me that the electric motordrive maybe 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 !
Question: 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 be replaced.
Has anyone else had this problem and how did he/she solve this ? Thanks in advance.
Sharky (the Netherlands)
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