1989 explorer 4.0 OHV.......observation and question

Do not mean to beat a dead horse here, but after reading pages and pages of the forum, it seem that most all vacuum leaks on the 4.0 OHV come from the upper intake "o" rings and very few from either the fuel rail or lower intake. If that is true, the upper repair is one I could handle. I have proved to myself it is the rear pair of intakes by the spray method.
So...the question is this: should I chance just repairing the upper or bite the bullet to the tune of $600+ for a complete intake repair?
The ol' girl only has 146,000 and is a rare stick shift with not a spec of rust. Advice is requested and appreciated.