Col... There must be a good few out there, all bitter and twisted, just like their owners who struggle to seal that Primary Case. I won't say BSA frames were made with today's laser precision and after all this time engine mounts, frames and crankcases can all have a degree of flexibility when it come to final assembly. This inner case is one area where a small difference at the front makes a big difference at the back and you can bet the average Joe, when faced with that gap between frame and case simply bolted it on nice and tight...under tension and ready to let go.
Any component installed with any element of strain is a top candidate for structural failure, hence broken mudguard stays, headlamp brackets etc. Always make the parts fit without strain and save hassle later.
I'll warm it up and see if it will flex back with a bit of a tweak before wasting time on the lug repair. Good to know a few smacks can do it when I lose my rag after being too gentle.
Cheers.
Swarfy.