Z didn't have any kind of washer, it was just metal to metal touching together. After I took it apart and cleaned things up I reassembled using a little RTV on the threads and where the metal to metal makes contact (at base).
I have an NA so boost leaks aren't an issue - but not the same with TTs. Just something to check out while you have it apart (fyi -- some units do have a thin nylon washer -- so be careful when you take your FICD solenoid apart)...