Seems like the F12 always had brown interiors, from the sources I can find, so brown it is. And yes, I am going to clean them up, since the seat bottoms aren't the most visible it felt easier to paint them on the sprue and touch them up later.
I started building the engine already during the spring. Since it seems like they were painted with most of the stuff assembled, there is not much detailing to do, everything should be green.
The frame was also assembled and painted during this spring. Red to match the striping on the cab.