At 5 years, I'd be looking at:
- group seal and shower screen
- group piston set. The lever cam followers are most likely worn and the seals will be on the way out
- check lever cam for wear
- valve grommets and lubrication
- lubricate group cam and most likely new cam o-rings
- We would also be checking for any other issues as reported by the client.
There is no "kit" available as such, but that doesn't mean that one couldn't be assembled for you.
Hope that helps.