[Big Ed]

Try a little heat?
Take the whole tube off and put in a vise?
If you get it off clean the threads and use a little Teflon tape when you put it back on.
Don't over tighten.
In guess you didn't put the cap on? The prior owner did? And over tightened it?

 

[Big Ed]

He fixed it as per post #16

"ended up just removing the pipe to drain the oil. re-installed as is. didn't want to spend the time to mess with it further. since oil only gets changed once per year, may just live with it. good to know some of the recommended solutions though."

One way to fix it I guess?