Just to expand, water pipes are apparently age related, according to everyone I have spoken to the plastic ages then dies. The kit has come down in prices I believe it is now £500 or so, it was more expensive when new.
I forgot the gearbox. It is an Aisin Warner box so very mainstream. They are scheduled an oil & filter change @ 120K I think but I had mine done early. I also had front/rear diffs & transfer box done at the same time. Another issue that some are seeing clunky gear changes, this is a valve block issue & can be pretty expensive. Only seems to apply to some cars though, some lowish miles other high miles.
Other issues are leaks, google bulkhead drains. Just done mine,
ing job but just time consuming. You mention tyres, I run winters & summers. My summers are 2+ years old & are Vredestein Vorti's. They were £600 a set when I fitted them & are at 5mm or so from 8mm when new. I had a geometry setup done when I had the tyres fitted & it was miles out. I suspect this is why people tear up tyres.
My winters are Dunlop Sport 5 in 18" (summers are 19") neither are N rated.
Brakes depends hugely on how you drive, most of mine is either very short 15 miles or so or long 100+ miles motorway. The rear brakes had been done the year before I got mine but both sets of discs are well lipped but I have 6mm of pad left. I suspect I will be doing front brakes in the next 6 months or so though.
Some Porsche Centres (OPCs) are prepared to work on them as Classics which means a lower labour rate. As a TIPEC member I get discounted bits as well.
The Kent TIPEC meet is next Monday at the Moody Mare West Malling. I should be there work permitting so you're welcome to have a nose around mine by all means.