NO!, no additives, which are friction modifiers, not good for wet clutches. I think once you have breather unplugged you should be all right.
I did the compression test with the throtle open and the engine warmed up this morning and it was over 17 bar on all 4 pistons. I unplugged the breathe tube from the air case. I hope that now it's all right.
17 bar is 246psi so that sounds very high to me. However if they are all close together, that's the most important thing. I still think you will find you are using oil. I doubt unplugging a breather is going to make much difference. Hope I'm wrong though.