Since the tweeter went out in one of my RTA11TL's I have gotten the but to tweak. I thank you all for you advice on X-over components. The advice will be put to good use.
CHECK SOLDER CONNECTIONS!
I did want to pass along something that I found when I opened up the speaker with the bad tweeter. The x-over utilizes a 4.4uF mylar in parallel with a 12uF electrolytic to produce the 16uF that is in series with the tweeter. The 4.4uF is soldered to the PCB and the 12uF is soldered to the leads of the 4.4uF. This is where I found a problem. One of the leads was inadequately (if at all) soldered causing an intermittent connection. This means that at times there was only the 4.4uF in series with the tweeter. The result is that lower frequencies would be allowed to pass to the tweeter and likely caused the failure.
1) The Daycron batting is apparently misplaced. Instead of being directly behind the MW6510's, both pieces are laying horizontally below the MW6510's. Over the years it may have fallen.
2) While testing the cabinet for resonance, I found that the wires that go from the x-over to the drivers was buzzing against the metal speaker baskets. I plan to secure the wires after I upgrade the x-overs.
3) The cabinet sides do tend to resonate and there is no side-to-side bracing. I'll probably add some bracing and some sound deadening material.
The replacement tweeters are on their way. I can update this thread as the project continues. I do welcome any advice.