I did a search (a quick one at that) for a similar topic, but didn't find a whole lot. Anyways, I have a Peugeot PGN10 Galibier (1986) that was very well kept on the outside. No dings, no chips, only some scratches (surface, these don't reach the metal) on the paint. Well, the fork was bent and the seatpost was stuck, but otherwise it was in great shape.

Now the main question, The internal rust isn't horrible, the seat tube was rusted, but it's not flaky. however, I am worried about one of the chainstays, because the rust is showing up around the vent holes and some of the flaky rust is sliding around and falling into the bottom bracket and vent holes. But it's only one side. Is this something to worry about? Perhaps the longevity of the frame is lessened by good factor? And is this something that could be replaced in the future?

And a picture:


Just the frame, it is currently built as a singlespeed (don't kill me It's just what I prefer, it didn't come with all the original components either).

Many thanks in advance