Brake Cylinder Seal (Rear)?

MOPAR Gods:

Is there suppose to be a seal between the backing plate and the brake cylinder on 9 in drum brakes? Just looked in the "blue" book (1968 Parts Catalog) and it shows p/n as 2534 663. Car is a 1968 Dodge Dart SL-6.
best.

Wher do you buy these seals??

Thank you so much. In another post MOPAR Gods clarified bolt dimensions for "tee" block attached to axle. MOPAR people are the best.