Excessive blow-by? Oily mess

About 2 months ago my wagon (diesel) started dripping oil at a much more considerable rate off the cross-member behind oil pan and also started pushing oil out the top of the dipstick tube.

Prior to this, I had none at dipstick tube and just a few drops here and there from the back of engine.

I'm thinking excessive blow-by, but have a few questions regarding this. She still starts, runs, performs very well along with fuel mileage seems unchanged. Also she doesn't smoke that much at all under normal driving down road. I do get some blue smoke upon start-up (which I assumed was leaking valve guide seals) and I get some black smoke under hard acceleration and load.

Things I've checked or done:
1. checked breather hose for clogging or obstruction - clear.
2. checked air filter, rotated orientation as I do get some oil
depositing in air cleaner housing.
3. replaced o-ring on dipstick to try to slow leak down.
4. performed "plugging breather tube test" as described on
this forum. engine shuts down in 2-3 seconds.
5. pulled oil fill cap off while running engine and observed
light but steady vapor puffing upwards from oil in valve
cover, along with tiny droplets of oil being blown out and
landing on top of valve cover.

My confusion is this; if I have worn piston rings and I do have excessive blow-by, shouldn't she be starting hard, running poorer and shouldn't she be blowing blue smoke out the exhaust?

I ran a post last week on the diesel discussion, but didn't come up with a lot of answers. For reference it's called "HELP - oil all over the place".

Would greatly appreciate anyone's help or advice. I am leaking at a rate of 1 qt. in about 250 miles. Prior to this I would typically burn 1 1/4 qts. in a 3000 mile interval, which I thought was good for an engine with almost 300k on.