One could always ask the seller about the placement of the clamp or possible crack. Compared to other French stencils of that era and equal quality, it's still a high price. We'll see how it goes.
There is definitely an undue "Buffet stencil" bias, IMO, for this era. R-13 era Buffets I understand the concept, but earlier Buffet clarinets? I don't have the direct experience necessary to inform me, but from what others report there were many early French makers that built clarinets of equal or better quality and these usually sell for less than anything rumored or known to be a Buffet stencil.
With the Marbeau, I'd like someone to compare one to a D. Noblet, a JTL, a Couesnon, an A. Robert, M. Lacroix, etc. If it is in a different universe, then the price is probably OK. If not, buy 2 of something else instead.