KZ1000J3 Rear Master Brake Cylinder Leak

Hello,
I just noticed some fluid on my exhaust and have traced it back to the rear master brake cylinder. There appears to be a slow leak at the bottom of it only while riding. It is where the piston assembly goes into the body. There is brake fluid on part 49016/B. Is this the result of a leak at the Ring, Dust Seal (part 43058)? Will replacing the dust seal correct the problem or do I need a rebuild kit. Not sure if this is an easy fix. Any comments would be appreciated. I just spoke to the shop I usually go to and they indicated a rebuild kit would likely be in order. Does Kawi sell these? I have looked in the Kawi and Clymer manual and I don't see a procedure to replace thiese parts. Also I gather I need to change the brake fluid with the fix or can I top it up after the seal and or rebuild kit is installed if this is the fix.? Right now the brake fluid level is low. Link to diagram of master cylinder is below.

www.partzilla.com/parts/search/Kawasaki/...+CYLINDER/parts.html

Many Thanks.

Sounds like a master cyl rebuild kit is in order Brent Probably the original one with a bunch of miles on it So its about time anyway. I think K and L make rebuild kits for our J bikes Made in Japan too. Not a big deal to rebuild either. Definately a project anyone can handle ,there is a snap ring on the lower end that gets removed then the whole piston comes out and gets replaced. Kawasaki sells the piston assembly part #43020-1035

Fluid is compressed inside the bore by the piston (403020), which has rubber cups to seal the piston against the inside of the bore.

Worn cups or pitted bore can provide an imperfect seal which allows fluid to escape backward past the cups and into the dust seal (which isn't expected to hold leaked fluid).

Sometimes a new replacement piston will arrest the leakage.
Sometimes a pitted bore may be dressed smooth and used with the existing piston, without leaking.

Regardless, I would suggest lightly dressing and smoothing the bore in order to reduce and minimize the effect of any pitting inside the bore.

Sometimes the bore is beyond restoration.

Reportedly, there are services available to re-line the bore, which effectively re-news the bore.
But might be more expensive than simply replacing the master cylinder.

A new replacement piston may be available from parts suppliers, such as Z1 Enterprises, or other on-line suppliers, including ebay. Would Google the part number that barney provided.

Good Fortune!

I'd remove the master from the bike and then open it up to inspect the bore before spending money on a piston kit (assuming one even exists). If the bore is pitted it's plan b time...