Front Brake - Master cylinder cap leak

Has anyone had a problem with brake fluid leaking out the cap of the master cylinder for their bike (kz900 front brake). I went for a ride yesterday and noticed moisture at the cap and just thought it was condensation for a while, but it's definitely fluid leaking at the cap. I got plenty on the paint but it didn't do any damage for some reason.

It's threaded right, and the gasket looks fine. I'll try some plumbers tape and see if that works for a short term solution. Any ideas? I guess I'll have to go fishing on ebay for a new one. Does anyone make a repop or am I stuck finding a 2nd hand unit?

Thanks

You can't seal the threads. I'm assuming you have the round style screw on cap, if you look at the cap you'll see it's slotted to allow air to enter the center of the accordian type rubber diaphram in the master cylinder. Air has to be allowed there so the accordian can stretch and compress to compensate for fluid level change from normal wear of the pads. The seal is the accordian rubber, so if leaking, look at it closely.

Thanks Ron,

It is the round cap style. I just went out and checked it. The accordian style seal/gasket looks great, as well as the hard plasic gasket that is in the top of the cap. I took it apart and put it back together. I'll give it another go tomorrow.