they use the same key of "Top Race Simulador 2009" that you can see when you launch the tool without arguments:
Code:
-k KEYN specify a keynum value different than the default one (0x000b2023)
        keynum is the NEEDED encryption number which is game dependent:
        0            rFator
        0x000b2023   Arca Sim Racing
        0x000b2023   ACTC Simulador Turismo Carretera
        0x000dfc2a   Top Race Simulador 2009
        0x0001be0b   Superleague Formula
indeed it's enough to use the following command to decrypt them perfectly:
Code:
rfactorgmdec -k 0x000dfc2a goma.tbc goma.tbc.decrypted