Just a suggestion,
Don't use gaskets with a motor plate. Use silicone rtv, and tighten it as tight as you like. Using gaskets, you can only tighten the plate up so tight before the gaskets get pushed out. Chassis flex will get them one day too.
Actually I o-ring the plate to the block - solves all the problems.
Looking at the picture , the o-ring depth looks pretty deep.
I'm an o-ring junkie. I o-ring anything that I can because its just so clean and does a great job of sealing. No mess to clean up when taking apart! I have yet to have anything leak that I have o-ringed as long as the o-rings are fresh (replaced the o-rings on the valve covers after about 12 years - they were due).
There are several configurations of o-ring grooves. The one I use is quite simple but has served me well. The groove dimension is straight out of the Parker o-ring manual. The one negative on this type of groove is the o-ring is loose and you have to use a dab of grease to keep from falling out during installation.
With my new cnc I am tempted to experiment with different types of grooves. Might on future projects.
