Replaced brake and gear cables on my son's friends MTB, and gave it a good old clean: checked the rear and front shifters ran cleanly, and gave the bike a good old lube. Old cables/inners were so rusted, that back brake did not even work - and he goes to school on this every day! Thought I had better intervene having witnessed the shocking state of the bike on a visit to our house a couple of weeks ago. Now running sweetly, so a good deed done.