I refurbished my brothers 1/24 S38, carefully taking the paint off the hull back to gel coat and repainted, it was a long old job. I repainted with a camouflage pattern. I recommend you purchase German S-Boats by Steve Wiper from Amazon, it has colour illustartions of the various camouflage patterns including the schnellbootweiss colour favoured for operations in the English Channel.
If the photo comes out you'll see my S100 type top and my brothers S38 bottom, I have many more photos of the S38 I can send you from the ragged state to the final finish. If you like to see them send me your e-mail dress in the pvt message facility on this website.
I'm also preparing a presentation on the design and development of S-boats for my local U3A Naval History Group.