It sounds like you have the intake manifold leak that seems to plauge LTx
engines in these cars. Look at the rear of the intake manifold, if there is a
trail of oil you have probably found your problem. This would also explain why
it takes about a week to reappear as it is generally a slow leak. There is a
TSB number 77-61-17 OCT 97 that tells about this problem. If you decide to
repair the leak try looking at
www.fl-fbody.com/members/bfranker/fbody/guides.htm.
FWIW I have the same problem on my 95 and I decide it was easier to clean up
the oil every couple of months, however mine is very small so it doesn't
smoke......
If this is truly the problem and you decide to just clean it when it gets dirty
do not get the optispark wet. It is not vented on the 94's and is pretty
expensive to repair.
Good luck.