Dunlavy SC IV A harsh high frequency

I have owned my SC IVA for many years. I replace the blown tweeters at least once a year. I know the original set were carefully matched at the factory but I can not duplicate the tecniques which John used in his shop to optimize response. The speakers sound glassy and I wonder if this is as a result of tweeters I have installed but would have been rejected by John. I have done a lot of work with room treatment,changing source, components, etc...
Are there any recommendations for fixing this issue?
Replace the Vifa tweeters with more expensive ones?
Thanks