So restoring Mini's is my job and I do 4 to 5 a year for customers. Some of these are what we class a bodyshell refurbishments and bolt back on the old parts but some like this one are full restorations.
It then got stripped to a bare shell and sent out for sand blasting. I didn't fancy spending a day in our booth and for the £500 it cost it was in my opinion worth it.
It came back from the blasters showing it's issues.
This highlighted the inner wings were rotten too so they got repaired, the inner and outer A panels came off to give access, they had rust in them too.
The red stuff? It's red oxide. Everything gets sand blasted to get rid of any rust, seems that will be welded get zinc weld thru primer and the rest that cant get reached later gets painted with red oxide before panels are welded on.