I double your money
For spares you could also ask Ruemema
Drehmaschinen von Ruemema
He is one of 2 I am aware of that is capable of rebuilding a 135 to original or better specs Also a very helpfull person
But be aware his solutions for a problem are always 110% Expensive many times therefore His machines can be discribed as conventional hard turning machines
IMO a repaint job on an old machine always looks worse than leaving the original paint. Unless. My vote is for cleaning the machine drastically and letting it be. If you go the Ruemema route and get the geometry back to better then new: then a repaint job (which takes ages when done right, and means dismantling to the rough castings etc.) might be in order.
Still: cleanup first, then assess. IMHO, of course.
50-60,0000 is madness for a 50 year old lathe, does not matter how accurate it is human error will be more of an issue IMO.
My experience with Schaublin as a company:
I could use some small parts for my 160s.
So I called their German location. They berated me for owning such old crap (I am not kidding), but told me to mail them the serial numbers and they would see if they could help me with some parts or a manual.
I mailed them the serial numbers and proceeded to never hear from them again.
Martin if you want I can supply you with a contact at Schaublin UK who is super helpful and I am sure will help you out on parts etc, he was very complimentary of my 1970 135 he only juddered when I mentioned I had a Hardinge HLV before