Anyone know who repairs or rebuilds woofers?

Stick with Bill, at Millersound.     You’d be hard-pressed to find someone more knowledgeable, or capable, regarding the repair of your speakers.     http://www.millersound.net/contact-bill-legall-millersound.html

If it's just reconing those services are fairly easy to find via a Google search.

I’d like to hear them!

Very specific cone design/construction.

Does OEM think the current larger woofer can work in that cabinet/crossover designed for original smaller woofer? If so, you would need to remove or protect the other drivers while a woodworker enlarged the holes. Ask OEM about the internal connections, if soldered, protection and carefully chosen woodworker is probably the way to go. Cutting wires, good insulated bullet connectors or soldered heat shrink connections could be successfully added in line as another option.

OEM might have an idea how to modify the existing crossover, OR, change the crossover. Many OEM's or Modifiers often upgrade the quality of crossover parts over the years, it might be a great synergistic change.

Perhaps you need ALL the specs of the original woofer, search for same size new woofer with near identical specs, to perform as close as possible with the crossover/other drivers, ...

Keep in mind, any larger woofer would normally be put in a larger enclosure for a cubic volume designed primarily for the woofer’s controlled response and balance to the other drivers, so knowing .. will not be the full answer.

My speakers, made 1958, 15" woofers, horn midrange, horn tweeter, in addition to OEM’s crossover, incorporated two OEM rheostats: Brilliance, and Presence.

That has helped me adjusting them in 4 different spaces, and moving the drivers to new custom enclosures. IF you find a near match, or OEM thinks their current slightly larger driver will work, perhaps suggest this ’presence’ rheostat idea, perhaps tame the larger woofer’s output bit by bit while listening in your space.

Luckily, replacement cones with the old cloth surrounds are available, I replaced the cones twice, once by a pro, once by me.

Rheostats: It must be said, balancing the frequency response L to R is not easy, I find my Mode switch on my McIntosh preamp the key to success, switching stereo to mono, all l, all r, l tor, r to l. And, Oscar Peterson’s Piano and Cassandra Wilson’s voice quite revealing. You don’t want any wandering at certain frequencies.

Perhaps a stereo crossover, specifically chosen for bass would be a better idea and eliminate the l/r matching issue. I cannot do that because the rheostats exist, and must be matched l/r prior to any stereo crossover.

Van L. Speakerworks in Chicago, IL...

http://www.vanlspeakerworks.com/

reconing is simple and easy, anyone  can do it,,, Thing is make sure you get the correct glue,,I made a  mess of the glue part, from usinga   glue from Home Depot, 
Messy, but works like brand new.
I think the issue was , the Seas excel has a  magnesium cone material,, and so glue just beaded up on the cone,,so should not be a  issue with any other woofer, just the <<world class- high tech>> magesium Excel cone material = not glue friendly..