"Sounds like the seals need to
"Sounds like the seals need to be replaced anyway.
Now that the engine is out, I'd repalce them both anyway, just because... and look at everything else you can't see when the engine is in the boat.
Regarding the crankcase ventilation, my 5.7L had two small diameter corrugated plastic tubes running from the valve covers and just kind of pointed toward the air cleaner/flame arrestor. I had significant leakage from the front main seal. It wasn't continuous, but if I'd run the engine at about 3000 rpm for about 30 minutes, I'd loose a quart of oil. There was some misalignment of the timing cover gasket, but even after I fixed that, I was still seeing a lot of leakage. The engine, at the time, was a brand new factory short block so I really wasn't ready to go after the front main seal. After realizing the crankcase wasn't being ventialted properly, I replaced the corrugated tubing with regular 1/2" hoses. I drilled a hole in the top of the air cleaner and glued a plastic 'T' in there and connected the hoses to that. I also put a PCV valve in each hose to prevent a backfire from causing a crankcase explosion. That was three years ago and I haven't leaked a drop of oil since."