GAR64, a fellow old car enthusiast with a '26 Willys Phaeton once told me to use corn meal, brush it in real good and vacuum it off. Haven't tried it myself but worth a try.
Is your Roadster top a LeBarron Bonney?? The grain looks different from what I recall them being,,maybe it's just the picture.
That is one advantage of a '29 Roadster with a black top!! Or a '30-'31 Standard Roadster!