I did the loop twice earlier today but I wasn't really trying. I rarely use the upper flipper as more than a guide unless the ball is coming down just right to shoot the loop with it otherwise its unpredictable where the ball will end up. I can see how it could be a multi shot loop but its not worth trying for more than shooting back up to the lanes.

When I play I use the left flipper for shooting the spinner
Right flipper for the left drop bank
Upper flipper for a guide
And never shoot the center drop bank

Good thing I saw this post I was planning on upgrading the flippers on mine too.