NAPA # is P4360 for the mc.
Just picked one up. $39.75
Core charge is $28.00, so I took the old one with me.
I think this fits 36-47?

More research! (right front wheel cylinder)
:cheer: Spoke with NAPA Brakes tech and they crossed the number over to #4804 Right or 4803 Left. 7/16x 20 inlet fitting that seals with a washer.
Fits various Pontiacs and 58-59 Cadillac Fleetwood - some up to 64
Will be Friday before it's in and then we will see!

[b]Raybestos WC4804 [/b] (34.81 at NAPA) + tax
OK-This is the right one, and here is the application list-
1958 - 1964 Cadillac
» 1958 - 1964 Cadillac DeVille (5 Vehicle Sub-Models)
» 1958 - 1959 Cadillac Eldorado (3 Vehicle Sub-Models)
» 1958 - 1964 Cadillac Series 60 Fleetwood (5 Vehicle Sub-Models)
» 1958 - 1964 Cadillac Series 62 (5 Vehicle Sub-Models)
» 1958 - 1958 Cadillac Series 70 Fleetwood Eldorado (1 Vehicle Sub-Models)
» 1958 - 1959 Cadillac Series 75 Fleetwood (2 Vehicle Sub-Models)

UPDATE---
New wc4804 installed and working fine