Not to hijack, but I've also been fighting a "losing a prime" issue and here's what I tried to eliminate it :

i. sealed swinging pickup threads and sealed bulkhead fitting to pan side ....no go
ii. replaced pickup to pump lines ....no dice
iii. replaced fittings....nope
iv. oil line loop at pump pump inlet....nada
v. lost the swinging pickup for a fixed pickup....no change
vi. new pump....better, but still took excessive time to prime after a shutdown of 1-2 days
vii. tried different filters......same crap

Lost patience pulling the dist to prime for fireup and lucked upon this at a real good price.....

Wish me luck.