Would you re-furbish an old ARC SP3a-1 ?

I have an old (circa 1974) ARC SP3a-1 preamp which basically does not work. It had some "un-documented" modifications done to it about 15 years ago. Is it worth the price to have ARC restore this classic and make it into an SP3c ? (The stated price for the upgrade is about $900, but they may charge more due to the un-documented modifications.) How would this then compare sonically to newer tubed preamps ?
PS I just re-checked the ARC web site. The price of the upgrade is $795 plus tubes. It is possible they might not even be willing to upgrade this particular unit, due to the modifications that were done. This is a "what if" question. Thanks, MBonn
You would be a whole lot better off if you learned to solder and did the work yourself as it is a job to rebuild one of these as all the resistors, caps, wiring, pot and more should be replaced....What you'll end up with is a very good unit with huge dynamics that is highly musical....I still use my SP3A-1 as a reference and plug it in from time to time to recall my life thirty years ago when I bought the unit....The unit is just fun to listen to....
Agree with Mr.Crump, rebuilt it back to stock spec with
the best parts you can afford. The owner's manual has all
the info you'll need.

If you want to sell it as is, please contact me.
Thanks for your feedback, Rcrump and Kana813. I don't plan on selling the ARC SP3a-1, if for no other reason than sentimental value. Unfortunately, I don't have the time to invest in this refurbish project myself, but I will probably send it off to ARC in the new year to see if they will tackle it. Thanks again for your input.