~~Here is a Rear Main Seal for your 1958 - 1962 Cadillac.
This will fit 365 & 390 Engines. 

Please Note: 1958 was a mid year change.  If you have Serial #:  50990 & up, this will work, If you have  #50989 or lower, it would be a different style.
 

1958 1959 1960 1961 1962