I've followed, well "lurked", in your threads since joining.
Was initially drawn to your screen name, as I also enjoy VAG & German vehicles in general.
Always impressed with your attention to detail.
Sorry I'm a little "late to the party" in this thread..
I have experience with finishing OSB (& Plywoods) in an automotive centric environments.
You made a good choice with the Zinsser Oil Base, I like the very similar Kilz Oil low odor.
I recommend a second coat (or even a third) of the Zinsser Oil Base, what you'll find is that each subsequent coat will do a few things for you -
1. (of course) hide more of the roller strokes & black lines the OSB has
2. smooth some of the heavy OSB texture
2a. this will also help down the road when you notice this "texture" likes to hold dust to the wall, especially in an workshop, making it look "dingy"
2b. less prone to moisture absorption
2c. less & easier final/top coating products
Speaking of top coating, see if our source for the Zinsser is willing to tint it for the coat before your top/final coat.
One OSB project I did was a 2 tone Lt & Dk Grey with a Royal Blue "belt" stripe.
I found that tinting the Kilz Oil Base very near to the final Lt & Dk colors really made the top/final coat of actual paint both go on super smooth, requiring less actual paint coats than previous areas with the same products.
Also had an added bonus for wear down the road/over the years in that if you have any light scuffs or spills you have to wipe up, the tinted base makes it so the "white" doesn't show through as much.
I hope that helps & feel welcome to PM me if you have any questions.
Keep on dubbin'
Matt