I've been a Toby Keith fan for awhile, and really like the song...
"I ain't as good as I once was, but I'm as good once as I ever was"
I watched on and off the TVLand Benson marathon (reminiscing), and
was surprised in the episode "Mid-Life Cowboy" when it was suggested
that Benson's cowboy name could be 'Rusty' when Benson replied,
"I ain't as good as I once was, but I'm as good once as I ever was"
I wondered if anyone could tell me for sure if Toby got the line from Benson,
or if it was just a happy coincidence?
Thanks.

I wish I had the answer for you, but I don't. I googled that quote. I thought that perhaps it was a from Shakespeare, Will Rogers, Dorothy Parker or another notable witty figure. I came up blank.

It's amazing to me that Toby Keith would use a line from a Benson episode, yet seems too striking to be a coincidence.

I've also just discovered a movie from 1940,
starring Clark Gable and Spencer Tracy,
called "Boom Town", it's about (surprise)
two oil well drillers and their changing fortunes...