Bad valve seals are more likely to allow oil to pass when engine is cold. Does it smoke more while warming up?
Piston rings.....hmmmm . Someone help me here. More likely to go hand in hand with low oil pressure caused by bearing wear, but not always. Look for oil coming into the EGR hose perhaps or oil coming from the tailpipe.
With 210,000, I'd lean toward the valve stem seals as the bottom end of the 2.3 is pretty damn tough. Just my thoughts....hope they help.
'07 R320 CDI " Manta Ray"
'62 300d Adenauer-350 Chevy
'12 VW Passat TDI 6/speed
'03 Dodge Ram 3500 - "Clifford, the big red Dodge" - Cummins w/6-speed
'68 Mustang fastback