"This brings up thing two. I removed the ridgid hose (tube) that goes from the crankcase to the turbo inlet. I found that the end that connects to the crankcase vent has split and, I'm sure, has been leaking.

Could this contribute to an oil leak that seems to be coming from the rear main seal?"

I don't think the cracked Crankcase Vent tube is contributing to the leak at the rear main seal. However, I would bet that you're due to clean the whole Crankcase Ventalation System. The tubes start to coke up with dried/burned oil and they restrict airflow. -and your rear crank seal is probably due to some higher than usual crankcase pressure and it would merit pulling the breather box off the engine (two 12mm or 13mm bolts holding it to the block, just below intake runners #3 and #4). Everybody knows about the flame trap issues on non-turbo cars, but both turbo and non-turbo cars eventually get plugged breather boxes, and I make it a habit to clean them every 100,000 miles. This usually entails boring the passegeways open with a screwdriver and smacking the boxes with a hammer handle to break up the solid matter inside them (followed by lots of shaking and then carb cleaner to get that stuff out). By decreasing the resistance to flow that your breather box is probably generating, you will probably reduce and possibly stop the leaking rear crank seal. It's worked wonders for me in stopping front camshaft leaks.

Regarding the split rigid hose from the Breather Box to the Turbo Inlet Hose, I've had acceptable results in taping up the split sections with electrical tape and patiently waiting for a suitable donor tube to show up in the local salvage yard.

I hope and pray you're lower end is ok, and I hope you don't have to pull the oil pan. I've pulled them before, but only on engines that were out of the vehicle.

God bless you and your engine,
Fitz Fitzgerald.
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'87 Blue 240 Wagon, 252k miles.
'88 Black 780, PRV-6, 146k miles.