The flywheel bolt holes in the crankshaft hub go all the way through to the crankcase, but unless you insist on using water-thin synthetic motor oil, it's not likely a properly-torqued bolt would allow any leakage. I would suggest using full-circle star-type lock washers on the flywheel bolts instead of split-style locks, however. A little dab of brush-on Permatex Super 300 wouldn't hurt- - - -it's a good thread lube as well as a sealer.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!