No longer able to fire nails and wondered if plunger/striker is sticking because I failed to add oil in-line with the air supply? Used to be that when the magazine was empty the nailer would leave a huge dent in the wood where the nail should have gone. Unit is firing but no evidence the plunger/striker is doing much good. Any ideas how to get it back on the air without replacing the unit? Too late to add the oil into the air inlet?

I would Oil up the front end and let it sit overnight. Then add the oil inline and fire away. Sounds like it may just need a little love.

The seals may be bad. The gun needs to be re-built. If your using the gun daily, its not uncommon for this to happen to the guns. Take it back to where you bought it or a store that sells your gun, they should be able to send it out to the factory for a rebuild. Some stores even have spare guns you can use why yours is out.