Hi Denzil,
To answer your question : to refurbish or replace with new, is simple, it depends
It depends on who will do the refurbishing and which new XO you would be considering.
One thing is for sure, they definitely need upgrading. If you refurbish you need some considerable experience with the different components and the effect they individually have on the sound. You do of course get to choose.
Having designed and built many speakers I know the time and effort you have invested in the impressive ones you have built and were it me, I would not hesitate to spend generously. The Tannoys deserve it.
If you buy you may get what the seller considers 'good enough'. I see Paul from RFC has been mentioned a few times and though I know nothing about this gentleman am sure he could advise you and use any component of your choice, should you have some specific item in mind.
I looked at the links you provided and at his board layout and it would not be too difficult for him to adapt it to accommodate a huge cap to the tweeter for example.
I see another poster is warning you about a cap's ESR
He claims replacing an electrolytic with the same value film cap will change the frequency response. This is simply not true.
A different value cap will alter the response but we are not considering doing that. The formula for Capacitive Reactance Xc = 1/2Pi.fc There is no value for R in the equation, so it is apparent that resistance can be ignored. Also consider that were this not true then every time you selected a different tweeter setting you would be changing the XO frequency.
Here is a link to a thread that I think will interest you. I have some pics showing an XO I built using a 6.8uf Jantzen Superior capacitor which is the same value used in the Tannoy gold. Its the big fat red one. The units I built for myself and friends used a mixture of Clarity Cap, Mundorf Supreme and Jupiter wax caps. I could not afford the very expensive Jupiters but maybe you can. They are delicious. The wire connecting to the speakers is the same Duelund I recommended you consider in your current speaker cable thread.
In my post 117 on page 12 there is a link that will take you to an excellent, almost a dissertation, on the sound of different caps and has been recently updated.
https://theartofsound.net/forum/show...efurb-s/page12
If you read on a few more pages you will find more pertinent info.
The link I provided on your speaker wire thread is a review by Jeff Day on the Duelund wire that he uses on his Altec VOTT and Tannoy Westminsters, I think. You can find a detailed discussion on his crossovers for both designs where he uses the eye-wateringly expensive Duelund caps. An entertaining read.
Originally Posted by Marco
Here are pics of the crossovers used in my 15" MGs:
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!!!put in an Aperiodic shelf and ALSO 3 ports, 4 inches x 10.5 inches, tuned to 29 Hz. I thought I would first hear what they sounded like with the Aperiodic shelf + the tuned ports (which I know is not usually done). Then I would experiment with taking the tubes off the ports so that they turned into simple Aperiodic cabinets. And then also experiment with taking the felt off the Aperiodic shelf and check what they sounded like as simple ported cabnet tuned to 29 Hz. However, Covid 19 and social distancing has put everything on hold. At the moment I have the shelf and the ports. And they actually sound very good, much, much better that the Lancaster cabinets they were originally in. I will experiment further without the shelf and just tuned ports and later without the tubes and just the Aperiodic shelf without the 19.5 inch tubes. 
Sound bloody good though, on the end of the valve amp in my avatar. Yes, with simply the standard Lockwood Aperiodic shelf, they sound best (in my smallish room), right into the corners and up against the back wall, then heavily toed-in towards the listening position)
One of the reasons I think the Lockwood Major cabs sound so good with 15" Tannoy DCs is their wide-baffle approach. 