I have overhauled about 20 right-hand levers. Not much point in overhauling the left levers, as you shift at least 10x as much on the right as the left, and the left levers never seem to need attention unless crashed.
As far as lube: any part of the shifter internals that are moving/rotating (such as the central shaft) and the G-springs should be lubed with grease. A light coating will do. I use standard marine-grease - not that the brand of grease matters.
Make sure that the G-spring carrier is not cracked: the
#1 cause of your symptoms. Next is worn-out springs. Third place is flattened G-springs, where the springs have been compressed or flattened by some process that I cannot explain. Perhaps they were installed backwards or crushed somehow. Finally, the spiral return spring might be tightened too much - it only takes 180 degrees of extra tension on the spring to cause this.
I have never seen the indexing ratchet ring worn out. Even on right levers that have been overhauled 4+ times. They are made of very hard steel.