Thoughts on replacing caps in 30 year old speakers

My point to asking Thiel is to see if you can find either a used or NOS replacement diaphram or driver. If it's a standard SS part then it would looking for it by the standard part number will give you more options to search for, but if it truly was a Thiel-only part then you're going to have to find a used or NOS replacement for the Thiel.

If I remember correctly,  this speaker uses mostly the higher voltage Solen Polypropylene caps, The 400 to 630v parts are pretty decent. If someone brought these to me to do, I would first recommend changing the series caps in the upper midrange and next the series cap in the tweeter and lastly the series caps in the lower midrange.... If your replacements are good enough,  you'll hear these changes in a positive manor.  I'm really not sure that changing anything else will make a marked difference.  These crossovers have some fairly extensive compensation circuitry,  but I really believe that you'll spend a ton to replace these comp parts with minimal if any improvement. (as long as the compensation parts are polyprop and 250v or higher) 
I hope this helps, Tim

I recap'd my 30 year old Magnat ribbon 5's with mundorf caps and while the tone stayed pretty true, the improvements across the board were very noticeable.

Well worth it

If it ain't broke, don't fix it!

I recently recapped a pair of Thiels along with an internal wire change..I say absolutely do it..I havent met a speaker yet that didnt improve on a recap !