hi,,
yes you have done your homework here, the rubber diaphrame in the diverter valve has perished and a small split has appeared between the pressure sides of the diaphram, you can buy a service kit but the bad news is its not worth the bother to renew, i strongly advise the complete diverter valve to be changed with a new unit and this is a proffesenal job. sadly no diy here, sorry......
terry ellis, January 2008