Hey David, nice job there! Very good work both on the Groove job (ain't it GREAT!) and your videos of the whole process. That's a Foredom w/ flex shaft isn't it? With experience you will learn to spot likely break-thru areas. I apply epoxy over those areas first. Either way before or after, as long as ya check your work w/ a flashlight, you'll catch 'em.
You are doing it right, like Ron teaches. Keep following Ron's teaching, we all here work together to advance the art and Science of the Groove. Sounds like you got Decent results. I like to sniff the exhaust on a hot engine before/after. I've found that if the power increases and the exhaust cleans up on hot engine, it's a Winner!
good on you, Brother!
Tracy G