Yeah the slave cylinders are made of cheese and they melt and warp, and it's a bugger to change. Worst on diesels and V6 but can happen on all of them so diesel autos became the 75 to have over here.
What spec/engine is it?
V6 head gaskets in 75s aren't as bad as the earlier handbuilt KV6 engines used in Rover 800s and the Kia Sedonas/Carnivals for head gasket issues, but they still have their fair share of problems like cracking thermostat housings (often leading to head gasket death) and sticking VIS motors. Also if it needs a timing belt change, run away - they have 3 and costs of getting on for £1000 are not uncommon.
Also if it's a 99 it should be a nice early Cowley built one with all the little pre-project drive bits.
As maffc says, the 1.8 K series despite it's reputation can be quite a sweet engine if it's been well maintained. Me and my best mate rescued a 1.8 75 from a scrapyard which had a magical K series, but that's a story for another thread. He later had one that had had the new MLS head gasket and revised oil rail which was one of the nicest running and sounding engines I've ever heard.
They're very flawed, but they can be lovely cars.