I recently acquired a 2000 Lesabre, 144,000 miles. 3.8 liter NA.
It was a Florida car, the body and interior are in great shape.
It uses some coolant, but I do not see a leak.
I plan to replace the elbows and upper intake and gasket.
It does idle a little rough, no codes present.
Do you think it would be necessary to replace the lower gaskets, while I have it apart, or not?

 

There were some problems with the EGR tube burning the phenolic intake manifold and causing coolant to leak out.
You might consider this;
Get hold of a cooling system pressure tester,pump up the system to no more than 15lbs and watch the gauge. If it goes down , start looking for leaks , water pump area , radiator hose connections,coolant recovery bottle, etc. If no leaks are found there is a possibility coolant is getting into the engine. The spark plug(s) may reveal which area the leak might be in. Make sure the engine oil does not appear "soupy". If it is , the leak is internal and the EGR tube area might be the problem..
You can usually rent a cooling system pressure tester from some auto supply stores.. Let us know what you find, thanks.

 

Do the manifold job, up and low. Use felpro gaskets and get the metal coolant elbows. Replace the man. too!