The old bloke at my co-op says he sometimes comes across BBs on French bikes slathered with this red goop he suspects is tubular cement, since it's a right bastard to clean off.

Is there a solvent for this stuff? Methylated sprits, maybe?

Goof off or goo gone

I'm wondering why would sewup tire glue end up in a BB??
If the glue is old and really dry and hard like amber, a Dremel with a wire brush tip will work very well to take it off. That's how I clean off old glue on my sewup rims.. It comes right off in clouds of glue dust, so try to use a mask if you can so you don't breath it in.

Chombi

is it red loctite?

I had a wheel with such a mess of hard red stuff I Paint stripped it-least damage to the aluminum

I suggest a little heat.

I have a can of glue solvent that I ordered from Branford Bike years ago. To be honest, it didn't work well on a pair of wheels that were plastered with red glue and had been stored for 20 years. It took a wire wheel to get them clean.

Yeah, I'm not surprised... that stuff goes damn hard.

Old French Loctite equivalent, maybe?