I'm not sure where this fit in since it seems more like a general question but here goes:

My old road bike that I've been redoing (a Peugeot 103) has an old seatpost with no rail clamp. The seat is fixed to it I believe. I thought it was a 25mm, and ordered a 25mm post from my LBS. It came in and when we tried to fit it, we found out that it was a 24mm.

Knowing that nobody makes those anymore (does anybody?), and I want to get a different seat on it, my LBS suggested and he's apparently done this before, but open up the tube by machining I think, 1mm to get the seatpost to fit.

I asked him if it would compromise the integrity of the steel frame and he told me it should be fine and that he's done this before. he did say that it was up to me however so no pressure there.

Does anybody know if this is a good idea or has done it? Or if anybody makes 24mm seatposts?

Thanks.