I always replace O-Rings for the reasons stated above...it is a PITA if they leak. Gaskets on a case by case...agree with everybody else about the replacement...it's more cheddar for the MoCo than anything else...(now that I say that, all my gaskets are gonna start leaking tomorrow!)..yeah I'm knocking on wood as I type

 

Same here! I reuse until they leak. Keep spares in my shop. Just don't overtorque them.

 

I do all of my own services. Gaskets and o-rings are cheap. I use new stuff every service.

 

Reuser here. I did change them when I put the chrome primary cover on. But when the time comes I will reuse them as well.