Tyres, Brakes and Suspension » Weeping fork seals

So my question is about weeping fork seals. I discovered after buying the bike that oil rings would be visible on the forks after maybe 50 or so miles of riding. The bike had 15k on the clock when I bought it. I had them replaced by a BMW dealer last year and they are weeping again.
The bike shows evidence of winter use with corrosion here and there but I don't see any damage or deterioration on the stanchions.
I've had other bikes with upside-downers but never seen this before. A quick internet search suggests maybe it's normal but I'm not convinced. Any thoughts out there?

My 2018 bike has had the same thing on both legs since new . I was going to ask about it while under warranty but COVID got in the way . It's only noticeable because dust sticks to the oil , I just live with it.

My 2016 RS has displayed these marks ever since I've had it (from April 2018). I'd rather they weren't there but I don't think it's an issue.

Yep, '17 here and about the same.

Thank you all. It's good to know you've had similar experiences. Incidentally, for stanchion above, read slider. Hard to believe I've been speaking English for well over 50 years now and still get the words wrong lol.