I use the locking block from the gun. It fits great and has always worked for me.

I have a UTG I bought on Amazon $10 and super heavy duty.

That “special tool” plus Kroil. Give it some time.

Rawny, ever find the right tool/trick?

I didn't see this when you originally posted (ironically, I was teaching the Shotgun block of an academy class that week) but I can send something that'll do the job if you're still stuck.