Ford #F5AZ-6700-A. $7 from fordpartsonline.com or Bill Jenkins.
These 2 can be found at rockauto.com
or BCA part# 482041N, Crankshaft Front Seal. $8.35
Fel-Pro Part# TCS45967 Crankshaft Front Seal $13.78
Don't know where that $25-50 is coming from.
BCA seal is $12.99 at Autozone
Fel-pro is $15.49
