Did you look at oil press. gauge when all this went down?
The reason I ask is, I once decided to treat my 340 to some synthetic.
Within a week or so I fired it up and heard rattling, looked at gauge, no pressure, wtf?
I dumped that oil, changed filter, put back in my 5w30 valvoline, wala, pressure came back.
No more synthetics for me. go figure...:coffee2: