A couple of nights ago I started up my Z (it has been standing for about a week) and found it didn't want to go into any gear. If I tried to select first it just made an unpleasant grinding sound. I pumped the clutch pedal a dozen times and it then went into first. I took it out and it drove fine - all gears selecting nicely. Parked it up for about two hours, got back in and everything still fine. Started it up again tonight after being stood two days and got the same thing happening again! Pumped clutch and it then went into gear. Driven fine again all night. Checked the reservoirs under the bonnet and all seem full. Can anyone advise what the problem might be before I take it to my trusty mechanic Warbo?