Engine Cooling problem
2003 Chevy Venture 6 cyl Front Wheel Drive Automatic 74200 miles
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I went to Goodyear and they did an analysis on my van. It is running hotter than normal. The told me it was losing coolant. They said it need an Intake Manifold Reseal (Intake Manifold Set), oil change/filter change, thermostat and distributer and O-Ring. Total estimate cost is $742.59. Parts total 166.68, labor 616.45 and some misc charges. They told me it takes 6 to 7 hours to do the work.

Should I get another estimate? Does this amount sound correct? Can I trust Goodyear to do a good job?
They told me Chevy vans have a problem with the intake leaking. It is not leaking on the ground, so it has to be leaking into some parts in my engine, etc.