KX Guru Racing

Here is another thing you can do ahead of time and prevent it from being a issue.
Relocate the vent off the back of the starter housing.
Some of these units will splash oil up and through the vent screen.
Messy

You unscrew the vent and replace it with a fitting.
Attach some hose and run it up and into your air box.
It's a easy fix.

I'm not 100% sure but I think the fitting is 1/8 NPT.

One other thing I did was to put some radiator hose over the top of the vent and I left the hose long and packed it with some foam to act as a additional filter.

It does not leak and no issues.
At some point I will likely change this to make it a bit more factory looking

O-RING replacement.
If you remove your starter very much, ie for jetting changes (yes it's way easier to remove the starter when making carb changes), you will loose that O-ring fairly quickly.

The cross section of the O-Ring is 3.2mm.
the ID is approximately 24mm.

The Inspection plate gasket is available direct from Cometic.
It's actually listed as a Honda number through Cometic but it's the same for the Kawasaki.
HON CR500 PANTHERA E-START .018" AFM STARTER CAP
EC2184018AFM