[ndutton]

Don't get so focused on the exhaust as the source of water incursion that you overlook the many other possibilities. Dave's advice regarding the addition of an anti siphon valve (see last paragraph) is of course spot on and many of us would like greater rise in the dry exhaust section but yours isn't that different from many here. It's good to eliminate the exhaust system as a possibility but thus far it's not conclusive that's the cause.

So what are the other possibilities for water mixing with oil? A common one is water pump seals. Another is manifold breach (I don't remember, have you pressure tested the manifold?). Head gasket, block and head casting issues are also possible but let's not go there unless further testing directs us.

My exhaust doesn't have an anti siphon valve but rather an anti siphon loop. It is placed in the same water injection hose well above the waterline but at the top of the loop is a small hose Tee'd in that runs to the galley sink drain. With this design there is no valve to service or fail.