So I got this "NOS" Moulton Fuse off of ebay. Not NOS (in painting all over the place), but
I am not too bent out of shape about that. I plan to ride it and it won't be as concerned now about damaging the paint. Might have bid less though.

Anyway, there is a line in the bottom side of the downtube near the BB. What do you think? Is that stress? Is it common to get damage there from an accident? As of now I don't see any other "stress" damage.

Looks like rust under the paint

I'd take some Jasco paint remover to that local area to see what's going on under the paint.

If the bicycle were allowed to sit outside in an environment where freezing temperatures are normal, at certain times of the year, water that finds it way inside of a bicycle frame will freeze. The water expands when freezing and with powerful force. I have seen my share of chain stays mushroomed out to the point where the tubing actually split.

Look elsewhere on the frame for bulging. Usually, the ice thing is most noticeable on the underside of the chain stays.

I am not saying that that is the case, in this instance, but it is one possibility. To that possibility, add this...

You might have better luck finding answers, if you show a big picture of the bicycle, so that we can see the profile. Crash damage can sometimes be determined by looking directly at the side of the bicycle.

+1: looks like a rust "spiderweb"...if you don't want to remove paint (and then do the touch-up) you might get away with just puncturing the 'web' with a sharp needle and applying acid (Phosphoric would be my choice) so it soaks in.
This may result in the paint directly over the web coming off, anyway, so you may want to have some touch-up at hand.

Well this is the whole frame, with a line showing where the line is.

Ya, I guess I am thinking it is just rust. But it is still good to get other opinions.

you could contact the builder... Dave Moulton still has a pretty active web presence.

Its nothing to worry about.

Could be a mark from a too tight clamp on cable guide...

Like he'd have the answer?

+1 Its rust.

If I paid ebay NOS type pricing, and got a frame that was clearly NOT NOS and with some signs of rust, I would be contacting seller immediately.

One of my pet peeves on ebay are sellers who misrepresent bike stuff as NOS. Now if you got what you think is a deal on it, move on and enjoy it.

You know I think the seller had it in his head that it was NOS. He was selling it because he hadn't thought about it in 7 years and just wanted it gone.
After I pointed out that it was not NOS (a number of photos made that clear) he quickly offered a partial refund. It is a unusual bike and a bit of rust won't kill the deal
for me. The refund was decent, so I am now on to figuring out what to do with the frame.

My Raleigh Competition had lines like that in the same location. I was sure they were cracks until I stripped the paint and found rust "spiderwebs". I had even thought about cutting it up and throwing it in the trash since I couldn't sell or even give away a cracked frame.

Good to know.

With rust like this one, I use a dremel carefully to expose the rust, and either spot treat, or go the full OA bath route. Assuming rust is just in this area, I would spot treat.

Looks kinda like an older repair. The Lug appears to look abraided as well as the tube between the lug and the line that is being refered to as the spiderweb. From the photo, it looks like the area has been repainted.

Ya, the repainting was the big clue on it not being NOS. There were a lot of repainted areas (well 10 or so small ones). The spider web area looks like original paint, the repainted area looks to me like a lot of the other repainted areas. Just covering up a paint ding.

+1 to rust. Reminds me of my Nishiki Competition, which definitely had "rust spider webs." It had a fair amount of rust when I bought it, and I gave it an Oxalic Acid bath, but the webs remained. unworthy1 also recommended a similar approach with mine (slitting open the spider web lines and, in my case, back in the OA bath). My Nishiki is/was in much worse condition, but the lines look very similar. My guess is there was a fair amount of rust which was treated to some extent and then disguised with touch up paint. Check out this link: Damaged paint - advice needed (rust removed, lines remain)

My "cracked" Competition looks like this now. It's one of my favorites.



Well, not quite. I was waiting for cable housings to arrive.

Well he might and it would be as good or better than any answer from this thread. At the very least I'm sure he'd appreciate that his frames seem to be generating some more interest, especially since the brand is being rebooted currently.