Originally Posted by
juvela
fender1 does not mention what the frame's seat binder arrangement is.
if, for example, it uses a welded seat lug with integral binder ears then this technique might be the ticket and problem may have nothing to do with seat tube itself.
It is this type:
https://www.google.com/search?q=Rive...GB1xdETDwhM%3A
I have filed and sanded the slot and ears from front and rear.