Dave
You will probably find that the teeth on the ratchet mechanism have worn in one place hence the intermittant problem.
You should not need to remove the water pump cover or seals If you remove the right hand casing with no damage to the seal you could also reuse the gasket with a smear of silicone around the water seal.
http://www.safemanuals.com/user-guid...EC%20250-_Ehis link
If you cannot dowload this let me have your e-mail and i will send you a copy.
It is a useful manual and will help you loads.
When you fit the kickstart mechanism place it in the recess then turn clockwise so the release arm slots behind the metal bracket. Then tension the spring (not too much) and slot into the hole.
Also there is a metal sleeve on the shaft with a cut out in it the cut out needs to be slotted over the inner spring . If you dont do this you wont have a hope in hell getting ur cover on.
short and sharp me laptops gonna die. Good luck Darren