Oh no, that is really bad news
Hope this can be verified that all is OK because the RH chain-set is such a centrepiece on this bike.
Moreso, it's got to be said this could all "escalate" quickly:
Let's say you are forced to look for a replacement, an original RH crank will be a nightmare to source and I dare not imagine the cost. Keeping it French and period wise correct means Stronglight and more tooling (what is to say the RH taper is compatible with Stronglight cranks?). There's also the pedal thread - Stronglight was available in 9/16" and French pedal thread. A move away from the French thread is not
such a bad thing, but you have the original pedals already. Many early AL cranks (regardless of brand) suffered breakages and so what is available and in good condition can be very costly indeed - the time period here is sadly not helpful. A lot of stuff can be in poor badly man-handled condition too.
I remember going a little crazy on this subject and having a few PMs with
@Guinessisgoodforyou and asking for advice elsewhere over what normally would have been a straight forward problem to fix after
finding a crack in an early lightweight chainring.
If this was my project, I would seriously consider a
complete steel cotter-pin chainset from a later mid-range donor French bike to get going. I'd give the TA Cyclotourist a good consideration mainly because of known robustness (even used on early MTB), no extra tooling and let's be honest would not be entirely out of place on a RH.
This is well worth reading too, because "underdog" brands like Nervar and Solida shouldn't be forgotten either if the budget is tight or the project not worthy ploughing in lots of money.
https://velo-orange.blogspot.com/2006/05/what-about-nervar.html
It is looking like that DS BB cup may need to come out after-all. If you were to move away from a French chainset, I think I would go with an early JIS Sugino.
