Sorry for the newbie question but do we need to renew the upper manifold gaskets every time? I removed the intake manifold to replace the o2 sensors and the current gaskets seem to be ok.

I have ordered the only the upper manifold gaskets with the intention of installing the lower manifold gaskets at a later date. Do I need new upper gaskets then?

 

I have successfully remove the manifold and reused the gaskets. The first go around I put in all new. You need to inspect and make sure they are soft and pliable, and there are no surfaces nicks or defects.
Worse case is you reuse them and one leaks and you have to go back in. The most important thing in dealing with the manifold is that the fasteners are removed cold and that you coat them with anti-seize compound. The fasteners screw into a brass insert pressed into the manifold and if they seize it is a big headache to replace.
Torquing in the correct order to to the correct tension is also very important.

 

Rogelio, no need to replace the gaskets every time you open up the manifold. Like was mentioned, if they are still pliable and not cracked, then you should be good. I would recommend using a little bit of say isopropyl alcohol or other suitable cleaner and wipe the surface where the gasket makes contact to make sure that you get any particles out of the way to ensure you get a good seal the first time.