Exhaust manifold mounting

[Djdawson2 at aol.com]

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Howdy,
I've had a few Audis at this point, almost all of which I've had the head off
of at one time or another.  Every time, I've replaced all the exhaust
manifold studs and nuts, and reused the washers.  My most recent was on my
200 20v, and during the process replaced the studs and nuts, and reused the
washers.  I replaced the stock manifold with an RS2 unit.
  While checking my oil this morning I noticed that 2 of the visible studs
are missing the nuts and washers.  This is 9k miles after replacement... and
this certainly isn't the first time this has happened to me.  Anyone have any
advice?  Should I be replacing the washers as well each time?  What can I do
to stop this?
Any advice greatly appreciated.
Dave