Hi Stephen,
If you catch them when they just start to leak they are re-build able with new seals and bearings, go on the French Gilera club 'rapid mous'e website there is a very detailed description giving bearing and seal numbers, if you didn't catch it early enough you could be making a new stainless shaft if the impeller is knackered or the housing damaged it gets really serious, you need a good machine shop to help
Good luck
John