My Mini was in fairly solid condition when I bought it, but it did have it some rust in the usual places.  I purchased a new pair of front wings a bonnet and the small panels that fit in front of the doors.  I welded the new panels on and sprayed them myself.

The gearbox had always been a bit awkward selecting second gear.  One day when I was driving back into the street where I live, the gearbox totally seized bringing the car to a sudden stop with squealing tyres.  The simplest fix was to buy a good second hand complete engine and gearbox from a local breakers yard and swap the whole lot over.  With the engine being so small on these cars,  I was able to lift the old one out and the new one in on my own in a very short amount of time.