I'm not a fan of Kohler, Briggs or any other vertical shaft air cooled engine, but don't make a decision when you are pissed. 600 hours doesn't sound like a lot but without knowing the history of those 600 hours, you really can't make a judgment as to whether the oil problem comes from bad design, faulty materials, or failure to perform required maintenance.
At this point, you have nothing to lose by performing a general autopsy (take off the heads) and you just might find the problem is something that's inexpensive and easy to fix. If it is, great. If not, just throw the pieces in a basket and take the whole shebang to the Floral Hills Lawnmower Cemetery (aka, junkyard).
edit: Oops, I see that you've owned it since the 100 hour mark. So you DO know the maintenance history...