I had two mini’s, an old 850 and then a 998cc city that became a 1380cc death trap.
They RUST, badly, shell and rear sub-frames. Radius arm bearings, swivel hub ball joints and wheel bearings were the main mechanical’s I experienced.
Stuck to the road like glue but when they did break free it was normally a trip into the bank or bushes (3 spring to mind).
Water pumps and rear brake slave cylinders were also prone to failure. Parts were usually cheap but remember a mates 1100 had an unusual set of slave cylinders as standard and they were 3 times the cost of the ones on my 998.
Great fun to drive but maintenance intensive if driven hard.
Get one with disks, drums all round are a bit scary.