That's why we missed it - it's #1 on the diagnostic list.

(We tend to overlook the obvious)
No drive in any selector position; cannot load engine.
Low oil level.
Clogged oil suction screen.
Defective pressure regulator valve.
Oil pump defective.
Input shaft broken.
Oil pump priming valve stuck.
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Looks like we might have a winner. Good luck, and happy shifting.
