The patch file for Real Fuels tries to patch part SSTU-SC-TANK-MUS-* which matches on no part currently existing in SSTU. Probably was looking for SSTU-SC-TANK-MUS.

https://github.com/shadowmage45/SSTULabs/blob/master/GameData/SSTU/ModIntegration/RealFuels/RF.cfg

I just made a PR to change it.