Wow! I cannot thank you guys enough for this thread. It took me five minutes and a couple bucks to get the lock shot dialed in. I simply put the magnetic tape on the left side of the metal guide.
Seems to be locked in. Didn't bounce out once after application.
Thanks again!!

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It's super simple my friend
I purchased 3/4 inch magnetic tape from lowes. Even though it said it had adhesive, I added a tape I have that is used for trophies. It's super thin and super strong double sided tape. I applied the magnetic tape only to the left guide, and only worked it back as far as I could reach. I didn't take anything off and I didn't prep the metal guide before applying the magnetic tape with added double sided tape.
Having the lock/extra ball shot locked in makes an already awesome game to play even better!