quick d18 rebuild question

I'm about to rebuild my d18 again (broke a bunch of teeth off the gears of my current one), and I have one question I never really figured out the first time around. Between the rear output housing and the case there is the stack of shims for endplay. How does one go about sealing that area up? Wouldn't gear oil theoretically leak out between each of the shims? And wouldn't any sealer that got put between all of them mess up the shim thickness?

 

I used copper gasket spray, and tried to adjust for a little extra spacing from it. It took me an iteration or two to get it in spec.

 

Yes and yes, but seems that folks put sealer in there anyway, and the added thickness doesn't affect the setting much.

If things are clean enough, you may be able to paint the outside edge of the shim pack with something to seal it. It seems like the model 20s I've had have been sealed from the factory with the original black paint. You might also be able to seal the edges after its together with a bead of silicone.