Use regular oil and change it (& filter) more frequently than normally
indicated for at least the first couple of changes after an overhaul.  There
is lots of metal particle matter generated during the break-in process.
IMHO the first oil & filter change in particular should be performed very
shortly after return to service.

In general and IMHO, the use of synthetic oil is most advantageous for use
in conditions of severe cold such as in the artic.  Gearboxes in particular
benefit because they seldom benefit from pre-operation heaters and do not
generate significant heat during operation.  This is more applicable to
vehicles using traditional gearlube than for Saturns using Dexron ATF as
gear lube in both transmission and differential.

There may be benefits from synthetic use in very hot climates but IMHO these
oils are not cost effective and their higher cost may cause users to extend
drain intervals longer than advisable.  IMHO clean oil is the best thing
that you can give any engine, particularly Saturns which are known to suffer
from clogged timing chain adjuster and sticking rings often caused by oil
change intervals that have been excessively extended..

Good luck, YMMV