mine would have been toast long ago.
I'm not discounting the idea that a good teacher can streamline your approach, but what I am saying is that dilligent and intropestive time on the horn often yields the same results, and it also grants a level of wisdom because you find out firsthand what does, and more importantly, what does not work.
I made one of my biggest strides in improvement my Freshman year of HS, and it wasn't because I had lessons with a private instructor, but rather simply because I LOVED playing my horn, and it was in my hands as much as possible every day. I wasn't even really practicing anything constructive from a method book - I was simply playing to play anything and everything in my repertoire of music - mainly my newfound love at the time, pep band charts. It's amazing how quickly technique improves when you have the horn in your hands for several hours a day and you are pushing your limits of technique.
And again, I don't think I'm an exception - I think anyone who had the same love of music and trumpet I did who put in the kind of time I did would see some substantial improvement, and I didn't need a teacher to tell me if what I was playing sounded right - I used my ears.