Once you complete 4th class transfer quest you get back certain amount of SP and *Items from your OE'd skills. (not sure exact name of this item, but some crystal)

  Regular GC need 2 of these *items.
  Mastery GC need 7 of these *items.

  on PTS, the amount of these items u get back from your OE'd skills are:
  2nd skill +30= 83
  3rd skill +15 = 35

  3rd OE table:
  +3 skill =0 *Items
  +4=1
  +5=1
  +6=2
  +7=3
  +8=4
  +9=5
  +10=7
  +11=9
  +12=10
  +13=19
  +14=24
  +15=35

  2nd OE'd skill:
  10 - 6
  11 - 7
  12 - 9  
  13 - 10
  14 - 12
  15 - 13
  16 - 15
  17 - 17
  18 - 19
  To get regular GC from Olympiad manager, you need:
  32,000 Oly token
  510,000 Fame
  35m Adena

  For Mastery GC:
  230,000 Oly Token
  3,700,000 Fame
  250m Adena