Sudden oil leak

[03 Big Red]

It doesn't seem possible that an oil leak this serious can start so suddenly. Shortly after my truck turned over 300,000 miles I noticed a slight oil burning smell at startup. In almost no time it's progressed to the point where my undercarriage is covered in oil and I leave a cloud of smoke behind me for the first two miles I Drive every morning. It's coming from the rear of the engine so the obvious assumption is rear main seal. But, is it possible for a rear main seal leak to develop so quickly? I read something that said a malfunctioning EGR can cause high pressure which dislodges the oil pan gasket. That sounds pretty far-fetched but when I checked, my EGR hose was collapsed. Obviously, changing the oil pan gasket or the rear main seal is a big job. Is there a way to diagnose this oil leak so that I don't do the wrong repair.
Thanks for your help.

 

[smokey]

Clean everything up and watch were it is leaking from.
After 300,000 seals and gaskets dry out or get hard and Crack and can cause a big leak in a short time.
Is the smoke coming out of the exhaust pipe or is just burning off the manifolds or pipes?

 

[CowboyBilly9Mile]

^^^ This, and take a look at the oil pressure sending unit.

 

[03 Big Red]

Thanks. It's burning off the exhaust pipes. There are shields directly under the leak that seem to collect oil overnight.
Where is the pressure sending unit?