I say Baloney.
Firstly, if the car was a full UK spec and purchased new, any problems would be covered under the 3yr warranty. Unless, of course, they were due to abuse; fried clutch, lack of engine oil etc. (or crashes).
Also, the Z doesn't have cambelts - it has timing chains which will generally last the life of the engine.
£6-7000 on modifications I could believe, but not on maintainence.