The Flash Gordon manual may have a mistake or two, I'm not sure. Either way, here's how I rubbered mine. There are 10 different rubber parts, for a total of 26 pieces.

Here's all the rubber you need for your Flash Gordon (all sizes are in inches and are inside diameter unless otherwise noted).

Qty	Item	Size
1	Shooter Tip	n/a
2	Flipper Rings	1-1/2"
4	Mini-Post Ring	7/16", OD
6	Rings	5/16"
2	Rings	3/4"
4	Rings	1"
1	Rings	1-1/2"
1	Rings	2"
2	Rings	2-1/2"
3	Rings	3"

And a description of each:

Item Qty Diameter (inches) Application Key Tip 1 Standard Ball Shooter Tip A Flipper Ring 2 1-1/2" Flippers B Ring 4 7/16", OD Mini-Post Rings C Ring 6 5/16" Post Ring D Ring 2 3/4" Between Tops of Ramps Below Targets E Ring 4 1" Small Flipper Misc F Ring 1 1-1/2" Behind 1-2-3 Drop Targets G Ring 1 2" Entrance to Left Spinner H Ring 2 2-1/2" Behind Lower Drop Targets Left Side of Saucer I Ring 3 3" Slingshots Front Edge of Upper PF J