A similar thing happened with my R before i blew it up last year, the slave cylender hoses went & before i had them replaced i had to put my foot behind the pedal and lift it up for it to work as you say it would engage but wouldnt come all the way back up if it is this then its gonna be a trip down to your local nissan garage for a replacment as i couldnt find any where else that made a replacement part i paid about £40 for them. hope this is of some help. Can anyone else shed some light on this?