I know it's 25-29% castor for old fox 35's and 22-23% castor/synth blend for newer ABC/ABN engines, but what about some of the old OS-S series, SuperTigre 35's, Veco 19-35's or Enya 15-35 ect?
I've been running the Power Master GMA 10/22 in them but not not sure that's the best fuel for them. What say you ?

Hi Clint
It is not  all castor for Foz 35s, they work even better  on part synthetic, I still have mine from the 1970s and they still are in great shape  after 100s of runs, and they are  not  black from burnt castor  goo.
I used 28& oil, with 1/4 synthetic in mine, it lubricates better, and keeps the engine cleaner, provides  longer life and  feels like they have better power over the life
Do NOT be  confused by people telling you that The  FOX 35  was designed  for castor only... The synthetics  we have did not  exist back then.
The  ONLY engine i would still use  all castor  in,  is  one that has burned on castor coating all over the side of the piston.

As far as your OLD  OS 30  35 S  engine  use the  exact same as the  FOX
For the  ST 35  they work well in a  1/2  syth  blend at  24 to 25 %, the ENYA engines will  work well with that mix  too, although  many run 20 to 22 % oil
For  others that do not have bushed  rods,  the  FOX blend  work well

You may want to read my engine article  posted  pinnned to the top of this forum

Randy