I use Castol GTX non-synthetic.  I wouldn't use any oil that came from
Pennsylvania stock (Pennsoil, Quakerstate, etc) because it has a parafin base
and causes sludging in the engine.  The oils that come from Texas stock don't
have this problem.
Learned this after talking with several engine rebuilders.
Sorry PA folks :(
Haven't gotten into the synthetic thing yet.  Maybe when I have the box
rebuilt (not far off with over 160k miles on her).

My 2 cents,
Ken Wilford
http://www.vanagain.com
John 3:16
Office (856)-765-1583
Shop (856)-327-0027
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