Well these folks found on a Google search claim it is 12mm x 1.50 pitch.
http://www.partsnmore.com/parts/suzuki/ls650/

There is a sealing washer...not sure if it is a crush washer or not.  I use mine each change and have not replaced it.....don't crank down on it hard and just make is snug.

The left cover does not have any sealing washers.....or any washers for that matter.  The gasket is supposed to seal and keep the oil away from the screws......and don't tighten them much....just snug as the bolts are small and they are threaded into aluminum.  It would be best to take the screw out, clean it, and apply a bit of sealer under the head if you have a leak.

Thx!
I was hoping it might be the same as the spark since I already have that tap...
Just want to clean it up some...

I'll try taking the single cover bolt out and maybe a little dab of sealant will help...don't really want to replace the cover gasket just yet...

Whenever I replace my cam chain (which probably won't be for a while) I'll cross that bridge and replace most of the gaskets...