Tappets? Common 150PD cam failure more like, it's chewing through its cam buckets and it'll need a new head if you're not careful. Rocker off and inspect lobes etc.
Blow boost pipes for fun. Eat lower engine (dogbone) mounts, wishbone bushes and rear beam bushes. Otherwise everything else common would have been fixed by now. Clutch and dual mass flywheel need looking at too. Can be clocked with a Gameboy and the power of your mind. Check the history thoroughly, I imagine it'll be known on uk-mkivs.net too, look at the 25th register.
On the whole the 150PD is a nice enough car, won't set your pants on fire, but it's well made and goes like hell with a 190BHP remap. They are getting old now though, I would insist on a specialist inspection.
The 25th Anniversary however is a slightly different animal. Lots of little tweaks and additions to make it a better car and they hold their money like you wouldn't believe. Completely different suspension, TT brakes, lots of stuff you wouldn't notice. I had mine for 3 years and lost a fraction over 2k on it. Your 197 is probably losing that in the next 12 months, this will have flattened out now and if you look after it, you'll probably sell it for what you paid.
No 197 dynamically, but a lot of car everywhere else.
