You don't actually say what the intermittent fault is - I presume that sometimes the motor fails to run when you operate the lever. If so it may well be the switch but that's just a guess...
Miles Tools & Machinery Centre, Yeovil UK, mtmc.co.uk supply spares for Qualcast machines and show exploded parts diagrams with part numbers for many models.
Good luck...
Peccavi
July 2009