Before ripping the engine apart, check three things.
1. The PCV port in the throttle body tends to carbon up in these engines. You still get some vacuum but not enough flow. You may have to remove the throttle body to get it really clean.
2. Pull the valve covers and check the oil return ports. Had 91 with same issue and found the return ports plugged solid with gunk. Cleaned out the ports and problem solved.
3. Replace PCV just on spec. Get one from the dealer. Their cheap and I have had a few bad ones right out of the box when buying aftermarket ones.
Only after checking these things would I start going deeper. For the price of a few gaskets its also good insurance. All of these things happen over time so its not a question of if, but rather a question of when.
91 Roadmaster Wagon, 6.2 diesel (gone but not forgotten)
91 Roadmaster Wagon, (gone to make toasters and refrigerators),
94 Fleetwood (thanks Fred) "Misty the tug boat" maybe the next diesel victim
05 Pontiac Grand Am...feeling less inadequate now
26 ft. Aerolite Cub Travel trailer