The motor is breathing its last - needs intensive care but may pass on even with the best attention...
Examine the brushes and armature - pretty certain to be in a poor state of health. New brushes and an armature clean up may restore some life but probably not for long.
My 17 year old Flymo is on its third motor - I buy spare ones from the guy at the council tip who collects mowers. A new motor will cost much more and a new mower even more than that.
BTW - tomorrow is June - most people have been cutting grass since March - get a grip...
This guy might have brushes...
http://www.carbonbrush.co.uk/
Good luck...
Peccavi
May 2009