This last year (2005) ths Buick Century was built ...3.1L V6 "couch on wheels" calls for 5W-30 on the oil fill cap ... Any reason why I can't run 0W-30 M1 Synthetic oil for a 6500 mile OCI with a Pure 1 filter for average around town driving ? ... With 118K miles on it my mechanic said the M1 0W-30 oil was a very nice all year oil although he felt it was not especially suited for a long OCI - your thoughts ?