Tried that, still the same.
So we took the whole mechanism to pieces, more WD40, white grease, all moving freely, but the motor is working intermittently and, like Richard's, only really working at all on the fast setting
So, looks like a trip to A8parts for a new motor...
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Present: S4 B8 avant, fully loaded, MRC Stage2, Milltek non-res, KW springs
Past: S8 D2 FL, S2 ABY coupe, RS6 C5 saloon, RS4 B7 saloon, S4 B5 saloon, S4 B6 avant, all gone but not forgotten