Aquallisa consealed cartridge shower. Seals or Cartridge?

Should i replace the Cartridge or Seals?

I have an Aqualisa shower, fitted in a new house 4 years ago, that has been dripping for several months but it's now getting worse.
Using the internet, i've looked for (and found) prices for replacement cartridges (it's the 22801 cartridge -approx £75!!).
Before i order and attempt to change the cartridge, could it be possible that i only really need replace the seals (seal kits approx £6)?

Thanks for any useful info.

Paul
November 2009